LintCode & LeetCode
  • Introduction
  • Linked List
    • Sort List
    • Merge Two Sorted Lists
    • Merge k Sorted Lists
    • Linked List Cycle
    • Linked List Cycle II
    • Add Two Numbers II
    • Add Two Numbers
    • Odd Even Linked List
    • Intersection of Two Linked Lists
    • Reverse Linked List
    • Reverse Linked List II
    • Remove Linked List Elements
    • Remove Nth Node From End of List
    • Middle of the Linked List
    • Design Linked List
      • Design Singly Linked List
      • Design Doubly Linked List
    • Palindrome Linked List
    • Remove Duplicates from Sorted List
    • Remove Duplicates from Sorted List II
    • Implement Stack Using Singly Linked List
    • Copy List with Random Pointer
  • Binary Search
    • Search in Rotated Sorted Array
    • Search in Rotated Sorted Array II
    • Search in a Sorted Array of Unknown Size
    • First Bad Version
    • Find Minimum in Rotated Sorted Array
    • Find Minimum in Rotated Sorted Array II
    • Find Peak Element
    • Search for a Range
    • Find K Closest Elements
    • Search Insert Position
    • Peak Index in a Mountain Array
    • Heaters
  • Hash Table
    • Jewels and Stones
    • Single Number
    • Subdomain Visit Count
    • Design HashMap
    • Design HashSet
    • Logger Rate Limiter
    • Isomorphic Strings
    • Minimum Index Sum of Two Lists
    • Contains Duplicate II
    • Contains Duplicate III
    • Longest Consecutive Sequence
    • Valid Sudoku
    • Distribute Candies
    • Shortest Word Distance
    • Shortest Word Distance II
  • String
    • Rotate String
    • Add Binary
    • Implement strStr()
    • Longest Common Prefix
    • Reverse Words in a String
    • Reverse Words in a String II
    • Reverse Words in a String III
    • Valid Word Abbreviation
    • Group Anagrams
    • Unique Email Addresses
    • Next Closest Time
    • License Key Formatting
    • String to Integer - atoi
    • Ransom Note
    • Multiply Strings
    • Text Justification
    • Reorder Log Files
    • Most Common Word
    • Valid Parenthesis String
    • K-Substring with K different characters
    • Find All Anagrams in a String
    • Find the Closest Palindrome
    • Simplify Path
  • Array
    • Partition Array
    • Median of Two Sorted Arrays
    • Intersection of Two Arrays
    • Intersection of Two Arrays II
    • Maximum Subarray Sum
    • Minimum Subarray Sum
    • Maximum Subarray II
    • Maximum Subarray III
    • Subarray Sum Closest
    • Subarray Sum
    • Plus One
    • Maximum Subarray Difference
    • Maximum Subarray IV
    • Subarray Sum Equals K
    • Intersection of Two Arrays
    • Intersection of Two Arrays II
    • Find Pivot Index
    • Rotate Array
    • Get Smallest Nonnegative Integer Not In The Array
    • Maximize Distance to Closest Person
    • Sort Colors
    • Next Permutation
    • Rotate Image
    • Pour Water
    • Prison Cells After N Days
    • Majority Element
    • Can Place Flowers
    • Candy
  • Matrix
    • Spiral Matrix
    • Set Matrix Zeroes
    • Diagonal Traverse
  • Queue
    • Design Circular Queue
    • Implement Queue using Stacks
    • Implement Queue by Two Stacks
    • Implement Stack using Queues
    • Moving Average from Data Stream
    • Walls and Gates
    • Open the Lock
    • Sliding Window Maximum
    • Implement Queue Using Fixed Length Array
    • Animal Shelter
  • Stack
    • Valid Parentheses
    • Longest Valid Parentheses
    • Min Stack
    • Max Stack
    • Daily Temperatures
    • Evaluate Reverse Polish Notation
    • Next Greater Element I
    • Next Greater Element II
    • Next Greater Element III
    • Largest Rectangle in Histogram
    • Maximal Rectangle
    • Car Fleet
  • Heap
    • Trapping Rain Water II
    • The Skyline Problem
    • Top K Frequent Words
    • Top K Frequent Words II
    • Top K Frequent Elements
    • Top k Largest Numbers
    • Top k Largest Numbers II
    • Minimum Cost to Hire K Workers
    • Kth Largest Element in an Array
    • Kth Smallest Number in Sorted Matrix
    • Kth Smallest Sum In Two Sorted Arrays
    • K Closest Points to the Origin
    • Merge K Sorted Lists
    • Merge K Sorted Arrays
    • Top K Frequent Words - Map Reduce
  • Data Structure & Design
    • Hash Function
    • Heapify
    • LRU Cache
    • LFU Cache
    • Rehashing
    • Stack Sorting
    • Animal Shelter
    • Sliding Window Maximum
    • Moving Average from Data Stream
    • Find Median from Data Stream
    • Sliding Window Median
    • Design Hit Counter
    • Read N Characters Given Read4 II - Call multiple times
    • Read N Characters Given Read4
    • Flatten 2D Vector
    • Flatten Nested List Iterator
    • Design Search Autocomplete System
    • Time Based Key-Value Store
    • Design Tic-Tac-Toe
    • Insert Delete GetRandom O(1)
  • Union Find
    • Find the Connected Component in the Undirected Graph
    • Find the Weak Connected Component in the Directed Graph
    • Graph Valid Tree
    • Number of Islands
    • Number of Islands II
    • Surrounded Regions
    • Most Stones Removed with Same Row or Column
    • Redundant Connection
  • Trie
    • Implement Trie
    • Add and Search Word
    • Word Search II
    • Longest Word in Dictionary
    • Palindrome Pairs
    • Trie Serialization
    • Trie Service
    • Design Search Autocomplete System
    • Typeahead
  • Trees
    • Binary Tree Inorder Traversal
    • Binary Tree Postorder Traversal
    • Binary Tree Preorder Traversal
    • Binary Tree Level Order Traversal
    • Binary Tree Zigzag Level Order Traversal
    • Binary Tree Vertical Order Traversal
    • N-ary Tree Level Order Traversal
    • N-ary Tree Preorder Traversal
    • N-ary Tree Postorder Traversal
    • Construct Binary Tree from Preorder and Inorder Traversal
    • Populating Next Right Pointers in Each Node
    • Populating Next Right Pointers in Each Node II
    • Maximum Depth of Binary Tree
    • Symmetric Tree
    • Validate Binary Search Tree
    • Convert Sorted Array to Binary Search Tree
    • Path Sum
    • Path Sum II
    • Path Sum III
    • Binary Tree Maximum Path Sum
    • Kth Smallest Element in a BST
    • Same Tree
    • Lowest Common Ancestor of a Binary Tree
    • Lowest Common Ancestor of a Binary Search Tree
    • Nested List Weight Sum II
    • BST Node Distance
    • Minimum Distance (Difference) Between BST Nodes
    • Closet Common Manager
    • N-ary Tree Postorder Traversal
    • Serialize and Deserialize Binary Tree
    • Serialize and Deserialize N-ary Tree
    • Diameter of a Binary Tree
    • Print Binary Trees
  • Segment Tree
    • Segment Tree Build
    • Range Sum Query - Mutable
  • Binary Indexed Tree
  • Graph & Search
    • Clone Graph
    • N Queens
    • Six Degrees
    • Number of Islands
    • Number of Distinct Islands
    • Word Search
    • Course Schedule
    • Course Schedule II
    • Word Ladder
    • Redundant Connection
    • Redundant Connection II
    • Longest Increasing Path in a Matrix
    • Reconstruct Itinerary
    • The Maze
    • The Maze II
    • The Maze III
    • Topological Sorting
    • Island Perimeter
    • Flood Fill
    • Cheapest Flights Within K Stops
    • Evaluate Division
    • Alien Dictionary
    • Cut Off Trees for Golf Event
    • Jump Game II
    • Most Stones Removed with Same Row or Column
  • Backtracking
    • Subsets
    • Subsets II
    • Letter Combinations of a Phone Number
    • Permutations
    • Permutations II
    • Combinations
    • Combination Sum
    • Combination Sum II
    • Combination Sum III
    • Combination Sum IV
    • N-Queens
    • N-Queens II
    • Generate Parentheses
    • Subsets of Size K
  • Two Pointers
    • Two Sum II
    • Triangle Count
    • Trapping Rain Water
    • Container with Most Water
    • Minimum Size Subarray Sum
    • Minimum Window Substring
    • Longest Substring Without Repeating Characters
    • Longest Substring with At Most K Distinct Characters
    • Longest Substring with At Most Two Distinct Characters
    • Fruit Into Baskets
    • Nuts & Bolts Problem
    • Valid Palindrome
    • The Smallest Difference
    • Reverse String
    • Remove Element
    • Max Consecutive Ones
    • Max Consecutive Ones II
    • Remove Duplicates from Sorted Array
    • Remove Duplicates from Sorted Array II
    • Move Zeroes
    • Longest Repeating Character Replacement
    • 3Sum With Multiplicity
    • Merge Sorted Array
    • 3Sum Smaller
    • Backspace String Compare
  • Mathematics
    • Ugly Number
    • Ugly Number II
    • Super Ugly Number
    • Sqrt(x)
    • Random Number 1 to 7 With Equal Probability
    • Pow(x, n)
    • Narcissistic Number
    • Rectangle Overlap
    • Happy Number
    • Add N Days to Given Date
    • Reverse Integer
    • Greatest Common Divisor or Highest Common Factor
  • Bit Operation
    • IP to CIDR
  • Random
    • Random Pick with Weight
    • Random Pick Index
    • Linked List Random Node
  • Dynamic Programming
    • House Robber
    • House Robber II
    • House Robber III
    • Longest Increasing Continuous Subsequence
    • Longest Increasing Continuous Subsequence II
    • Coins in a Line
    • Coins in a Line II
    • Coins in a Line III
    • Maximum Product Subarray
    • Longest Palindromic Substring
    • Stone Game
    • Burst Balloons
    • Perfect Squares
    • Triangle
    • Pascal's Triangle
    • Pascal's Triangle II
    • Min Cost Climbing Stairs
    • Climbing Stairs
    • Unique Paths
    • Unique Paths II
    • Minimum Path Sum
    • Word Break
    • Word Break II
    • Range Sum Query - Immutable
    • Decode Ways
    • Edit Distance
    • Unique Binary Search Trees
    • Unique Binary Search Trees II
    • Maximal Rectangle
    • Maximal Square
    • Regular Expression Matching
    • Wildcard Matching
    • Flip Game II
    • Longest Increasing Subsequence
    • Target Sum
    • Partition Equal Subset Sum
    • Coin Change
    • Jump Game
    • Can I Win
    • Maximum Sum Rectangle in a 2D Matrix
    • Cherry Pick
  • Knapsack
    • Backpack
    • Backpack II
    • Backpack III
    • Backpack IV
    • Backpack V
    • Backpack VI
    • Backpack VII
    • Coin Change
    • Coin Change II
  • High Frequency
    • 2 Sum Closest
    • 3 Sum
    • 3 Sum Closest
    • Sort Colors II
    • Majority Number
    • Majority Number II
    • Majority Number III
    • Best Time to Buy and Sell Stock
    • Best Time to Buy and Sell Stock II
    • Best Time to Buy and Sell Stock III
    • Best Time to Buy and Sell Stock IV
    • Two Sum
    • Two Sum II - Input array is sorted
    • Two Sum III - Data structure design
    • Two Sum IV - Input is a BST
    • 4 Sum
    • 4 Sum II
  • Sorting
  • Greedy
    • Jump Game II
    • Remove K Digits
  • Minimax
    • Nim Game
    • Can I Win
  • Sweep Line & Interval
    • Meeting Rooms
    • Meeting Rooms II
    • Merge Intervals
    • Insert Interval
    • Number of Airplanes in the Sky
    • Exam Room
    • Employee Free Time
    • Closest Pair of Points
    • My Calendar I
    • My Calendar II
    • My Calendar III
    • Add Bold Tag in String
  • Other Algorithms and Data Structure
    • Huffman Coding
    • Reservoir Sampling
    • Bloom Filter
    • External Sorting
    • Construct Quad Tree
  • Company Tag
    • Google
      • Guess the Word
      • Raindrop on Sidewalk
    • Airbnb
      • Display Pages (Pagination)
    • Amazon
  • Problem Solving Summary
    • String or Array Rotation
    • Tips for Avoiding Bugs
    • Substring or Subarray Search
    • Sliding Window
    • K Sums
    • Combination Sum Series
    • Knapsack Problems
    • Depth-first Search
    • Large Number Operation
    • Implementation - Simulation
    • Monotonic Stack & Queue
    • Top K Problems
    • Java Interview Tips
      • OOP in Java
      • Conversion in Java
      • Data Structures in Java
    • Algorithm Optimization Tips
  • Reference
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On this page
  • Array Concepts
  • Array
  • Dynamic Array
  • 2D Array - Matrix
  • Array Basic Operations
  • Iterate Through Loop in Java
  • Conversion between Array and ArrayList in Java
  • Sliding Window
  • Prefix Sum
  • Kadane's Algorithm

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Array

Array Concepts

Array

An array is a basic data structure to store a collection of elements sequentially . But elements can be accessed randomly since each element in the array can be identified by an array index.

Dynamic Array

... an array has a fixed capacity and we need to specify the size of the array when we initialize it. Sometimes this will be somewhat inconvenient and wasteful. Most programming languages offer built-in dynamic array which is still a random access list data structure but with variable size. For example, we have vector in C++ and ArrayList in Java.

Operations in Dynamic Array

// "static void main" must be defined in a public class.
public class Main {
    public static void main(String[] args) {

        // 1. initialize
        List<Integer> v0 = new ArrayList<>();
        List<Integer> v1;                           // v1 == null

        // 2. cast an array to a vector
        Integer[] a = {0, 1, 2, 3, 4};
        v1 = new ArrayList<>(Arrays.asList(a));

        // 3. make a copy
        List<Integer> v2 = v1;                      // another reference to v1
        List<Integer> v3 = new ArrayList<>(v1);     // make an actual copy of v1

        // 3. get length
        System.out.println("The size of v1 is: " + v1.size());

        // 4. access element
        System.out.println("The first element in v1 is: " + v1.get(0));

        // 5. iterate the vector
        System.out.print("[Version 1] The contents of v1 are:");
        for (int i = 0; i < v1.size(); ++i) {
            System.out.print(" " + v1.get(i));
        }
        System.out.println();
        System.out.print("[Version 2] The contents of v1 are:");
        for (int item : v1) {
            System.out.print(" " + item);
        }
        System.out.println();

        // 6. modify element
        v2.set(0, 5);       // modify v2 will actually modify v1
        System.out.println("The first element in v1 is: " + v1.get(0));
        v3.set(0, -1);
        System.out.println("The first element in v1 is: " + v1.get(0));

        // 7. sort
        Collections.sort(v1);

        // 8. add new element at the end of the vector
        v1.add(-1);
        v1.add(1, 6);

        // 9. delete the last element
        v1.remove(v1.size() - 1);
    }
}

2D Array - Matrix

In some languages, the multidimensional array is actually implemented internally as a one-dimensional array while in some other languages, there is actually no multidimensional array at all.

1. C++ stores the two-dimensional array as a one-dimensional array.

So actually A[i][j] equals to A[i * N + j] if we defined_A_as a one-dimensional array which also contains M * N elements.

2. In Java, the two-dimensional array is actually a one-dimensional array which contains M elements, each of which is an array of N integers.

The picture below shows the actual structure of a two-dimensional array A in Java:

Array Basic Operations

Iterate Through Loop in Java

package crunchify.com.tutorial;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

/**
 * @author Crunchify.com
 */

public class CrunchifyIterateThroughList {

    public static void main(String[] argv) {

        // create list
        List<String> crunchifyList = new ArrayList<String>();

        // add 4 different values to list
        crunchifyList.add("eBay");
        crunchifyList.add("Paypal");
        crunchifyList.add("Google");
        crunchifyList.add("Yahoo");

        // iterate via "for loop"
        System.out.println("==> For Loop Example.");
        for (int i = 0; i < crunchifyList.size(); i++) {
            System.out.println(crunchifyList.get(i));
        }

        // iterate via "New way to loop"
        System.out.println("\n==> Advance For Loop Example..");
        for (String temp : crunchifyList) {
            System.out.println(temp);
        }

        // iterate via "iterator loop"
        System.out.println("\n==> Iterator Example...");
        Iterator<String> crunchifyIterator = crunchifyList.iterator();
        while (crunchifyIterator.hasNext()) {
            System.out.println(crunchifyIterator.next());
        }

        // iterate via "while loop"
        System.out.println("\n==> While Loop Example....");
        int i = 0;
        while (i < crunchifyList.size()) {
            System.out.println(crunchifyList.get(i));
            i++;
        }

        // collection stream() util: Returns a sequential Stream with this collection as its source
        System.out.println("\n==> collection stream() util....");
        crunchifyList.forEach((temp) -> {
            System.out.println(temp);
        });
    }
}

Conversion between Array and ArrayList in Java

From Array to ArrayList

// java.util.ArrayList

Element[] array = {new Element(1),new Element(2),new Element(3)};

// 1. Most popular and accepted answer
ArrayList<Element> arrayList = new ArrayList<Element>(Arrays.asList(array));

// Next popular answer
List<Element> list = Arrays.asList(array);
// Cons: It is not the best, because the size of the list returned from asList() is fixed

From ArrayList to Array:

// Method 1: Using Object[] toArray() method


// (Preferred) Method 2: Using T[] toArray(T[] a)
// a − This is the array into which the elements of the list are to be stored, 
// if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.
// java.util.ArrayList.toArray(T[])

ArrayList<Integer> foo = new ArrayList<Integer>();
foo.add(1);
foo.add(1);
foo.add(2);
foo.add(3);
foo.add(5);

Integer[] bar = foo.toArray(new Integer[foo.size()]);

System.out.println("bar.length = " + bar.length);


// Method 3: Using get() in for loop manually

For example, suppose thatcis aCollection. The following snippet dumps the contents ofcinto a newly allocated array ofObjectwhose length is identical to the number of elements inc.

Object[] a = c.toArray();

Suppose thatcis known to contain only strings (perhaps becausecis of typeCollection<String>). The following snippet dumps the contents ofcinto a newly allocated array ofStringwhose length is identical to the number of elements inc.

String[] a = c.toArray(new String[0]);

Sliding Window

A sliding window is an abstract concept commonly used in array/string problems. A window is a range of elements in the array/string which usually defined by the start and end indices, i.e. [i,j) (left-closed, right-open). A sliding window is a window "slides" its two boundaries to the certain direction. For example, if we slide [i, j)to the right by 11 element, then it becomes [i+1, j+1) (left-closed, right-open).

Prefix Sum

Prefix sum 数组的 local / global 通用模板,求 min / max 皆可,使用时需要注意初始条件以及顺序:

        int[] leftMax = new int[n];
        int prefixSum = 0;
        // 代表从起始位置开始,值最小的连续和数组
        int localMin = 0;
        int globalMax = Integer.MIN_VALUE;
        for(int i = 0; i < n; i++){
            prefixSum += nums[i];
            globalMax = Math.max(globalMax, prefixSum - localMin);
            localMin = Math.min(localMin, prefixSum);

            leftMax[i] = globalMax;
        }

Kadane's Algorithm

Kadane's Algorithm 相比 prefix sum 的特点是,必须要以 nums[0] 做初始化,从 index = 1 开始搜,优点是在处理 prefix product 的时候更容易处理好“-1” 和 “0” 的情况。

这类靠 prefix sum/product 的 subarray 问题,要注意好对于每一个子问题的 local / global 最优解结构,其中 local 解都是“以当前结尾 && 连续”,而 global 未必。

public class Solution {
    public int maxSubArray(int[] nums) {
        if(nums == null || nums.length == 0) return 0;

        int localMax = nums[0];
        int globalMax = nums[0];
        for(int i = 1; i < nums.length; i++){
            localMax = Math.max(nums[i], localMax + nums[i]);
            globalMax = Math.max(globalMax, localMax);
        }

        return globalMax;
    }
}

*Subarray Sum 系列问题参考:

PreviousSimplify PathNextPartition Array

Last updated 5 years ago

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Excepts from LeetCode:

The picture below shows the actual structure of an M * N array A:

The following from source:

Source:

https://leetcode.com/explore/learn/card/array-and-string/202/introduction-to-2d-array/1166/
Five ways to Iterate Through Loop in Java
https://dzone.com/articles/how-convert-array-arraylist
https://www.geeksforgeeks.org/arraylist-array-conversion-java-toarray-methods/
https://stackoverflow.com/questions/7969023/from-arraylist-to-array
https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html
https://docs.oracle.com/javase/tutorial/collections/interfaces/collection.html
https://mnmunknown.gitbooks.io/algorithm-notes/626,_dong_tai_gui_hua_ff0c_subarray_lei.html