Algorithms
  • Introduction
  • Analysis of Algorithms
  • Numbers
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      • Pow(x, n)
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      • Intersection of Two Arrays
      • Intersection of Two Arrays II
      • Two Sum II - Input array is sorted
      • Find the Duplicate Number
    • Longest Common Prefix
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      • Implement strStr()
      • Add Binary
      • Duplicate Counts
      • Find Duplicates
      • Reverse String
      • Array Partition I
      • Two Sum II - Input array is sorted
      • Remove Element
      • Max Consecutive Ones
      • Minimum Size Subarray Sum
      • Reverse Words in a String
      • Reverse Words in a String III
      • Remove Duplicates from Sorted Array
      • Move Zeroes
      • Rotate Array
      • Rotate Image
      • Best Time to Buy and Sell Stock
      • Best Time to Buy and Sell Stock II
      • Valid Anagram
      • 3Sum
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      • Count and Say
      • Merge Sorted Array
      • Shuffle an Array
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      • Design Linked List
      • Design Doubly Linked List
      • Find Middle Element
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      • Find Nth Element from End
      • Remove Nth Node From End of List
      • Add Two Numbers
      • Merge Two Sorted Lists
      • Remove Nth Node From End of List
      • Reverse Linked List
      • Remove Linked List Elements
      • Odd Even Linked List
      • Design Doubly Linked List
      • Flatten a Multilevel Doubly Linked List
      • Rotate List
      • Copy List with Random Pointer
      • Insert into a Cyclic Sorted List
      • Delete Node in a Linked List
      • Palindrome Linked List
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      • Intersection of Two Arrays
      • Single Number
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      • Contains Duplicate II
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      • Longest Substring Without Repeating Characters
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      • Valid Sudoku
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      • First Unique Character in a String
      • Intersection of Two Arrays II
      • Logger Rate Limiter
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      • Group Shifted Strings
      • Find Duplicate Subtrees
      • 4Sum II
      • Top K Frequent Elements
      • Unique Word Abbreviation
      • Insert Delete GetRandom O(1)
    • Binary Tree
      • Binary Tree Preorder Traversal
      • Binary Tree Inorder Traversal
      • Binary Tree Postorder Traversal
      • Binary Tree Level Order Traversal
      • Maximum Depth of Binary Tree
      • Symmetric Tree
      • Path Sum
      • Balanced Binary Tree
      • Count Univalue Subtrees
      • Construct Binary Tree from Inorder and Postorder Traversal
      • Construct Binary Tree from Preorder and Inorder Traversal
      • Populating Next Right Pointers in Each Node
      • Lowest Common Ancestor of a Binary Tree
      • Serialize and Deserialize Binary Tree
      • Median of Two Sorted Arrays
      • Invert Binary Tree
      • Find K-th Smallest Pair Distance
      • Split Array Largest Sum
    • Heap
    • Binary Search Tree
      • Validate Binary Search Tree
      • Inorder Successor in BST
      • Binary Search Tree Iterator
      • Search in a Binary Search Tree
      • Insert into a Binary Search Tree
      • Delete Node in a BST
      • Kth Largest Element in a Stream
      • Lowest Common Ancestor of a Binary Search Tree
      • Contains Duplicate III
      • Height-Balanced BST
        • Balanced Binary Tree
        • Convert Sorted Array to Binary Search Tree
    • Map
    • N-ary Tree
      • N-ary Tree Preorder Traversal
      • N-ary Tree Postorder Traversal
      • N-ary Tree Level Order Traversal
      • Maximum Depth of N-ary Tree
      • Encode N-ary Tree to Binary Tree
      • Serialize and Deserialize N-ary Tree
    • Trie
      • Implement Trie (Prefix Tree)
      • Map Sum Pairs
      • Replace Words
      • Design Search Autocomplete System
      • Maximum XOR of Two Numbers in an Array
      • Add and Search Word - Data structure design
      • Word Search II
      • Word Squares
      • Longest Common Prefix
      • Palindrome Pairs
    • Balanced Tree
      • B-Tree
      • Red-black Tree
      • AVL Tree
    • Graph
      • A* Search
      • Breadth First Search
      • Depth First Search
      • Dijkstra Algorithm
  • Sequences
    • Fibonacci Sequence
  • Dynamic Programming
    • Knapsack problem
    • Climbing Stairs
    • Best Time to Buy and Sell Stock
    • Maximum Subarray
    • House Robber
  • Interviews
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      • Repeated String Match
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      • Next Closest Time
      • Longest Univalue Path
      • License Key Formatting
      • Spiral Matrix
      • Plus One
      • Trapping Rain Water
      • Longest Substring with At Most K Distinct Characters
      • Add Bold Tag in String
      • Game of Life
      • Read N Characters Given Read4
      • Read N Characters Given Read4 II - Call multiple times
      • One Edit Distance
      • Valid Palindrome
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      • Valid Parentheses
      • Image Smoother
      • Intersection of Two Arrays
      • Max Consecutive Ones
      • Max Consecutive Ones II
      • Shortest Palindrome
      • First Missing Positive
      • First Unique Character in a String
      • Move Zeroes
      • Remove Duplicates from Sorted Array
      • Merge k Sorted Lists
      • Insert into a Cyclic Sorted List
      • Evaluate Division
      • Inorder Successor in BST
      • Robot Room Cleaner
      • Redundant Connection II
      • Course Schedule
      • Validate Binary Search Tree
      • Closest Binary Search Tree Value
      • Word Squares
      • Strobogrammatic Number II
      • Word Search II
      • Android Unlock Patterns
      • Minimum Window Substring
      • Kth Largest Element in an Array
      • Shortest Distance from All Buildings
      • Find K-th Smallest Pair Distance
      • Find K Pairs with Smallest Sums
      • Range Module
      • Insert Interval
      • Sort Transformed Array
      • Merge Intervals
      • Longest Palindromic Substring
      • Next Greater Element I
      • Pacific Atlantic Water Flow
      • Evaluate Reverse Polish Notation
      • Decode Ways
      • Word Break
      • Sentence Screen Fitting
      • Maximum Vacation Days
      • Edit Distance
      • Minimum Path Sum
      • House Robber II
      • Moving Average from Data Stream
      • Peeking Iterator
      • Binary Search Tree Iterator
      • Zigzag Iterator
      • Design Tic-Tac-Toe
      • Range Sum Query 2D - Mutable
      • UTF-8 Validation
      • Maximum Product of Word Lengths
  • Other
    • Game of Life
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  • Add Binary
  • Solution

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  1. Data Structures
  2. Array & List

Add Binary

Add Binary

Given two binary strings, return their sum (also a binary string).

The input strings are bothnon-emptyand contains only characters1or 0.

Example 1:

Input: a = "11", b = "1"
Output: "100"

Example 2:

Input: a = "1010", b = "1011"
Output: "10101"

Solution

class Solution {
    public String addBinary(String a, String b) {
        // read from right side (from both strings) until 0
        // convert them to inteteger and add cary, if 3, write 0 and cary 1, if 2 write 0 cary 1, if 1 write 1, else write 0
        List<Character> chars = new ArrayList<>();
        int aIndex = a.length() - 1;
        int bIndex = b.length() - 1;
        int carry = 0;
        while (aIndex >= 0 || bIndex >= 0) {

            int aNum = aIndex >= 0 ? (a.charAt(aIndex) - 48) : 0;
            int bNum = bIndex >= 0 ? (b.charAt(bIndex) - 48) : 0;
            int sum = aNum + bNum + carry;

            if (sum == 3) {
                chars.add('1');
                carry = 1;
            } else if (sum == 2) {
                chars.add('0');
                carry = 1;
            } else if (sum == 1) {
                chars.add('1');
                carry = 0;
            } else {
                chars.add('0');
                carry = 0;
            }

            aIndex--;
            bIndex--;
        }
        if (carry == 1) {
            chars.add('1');
        }
        StringBuilder sb = new StringBuilder();
        for (int i = chars.size() - 1; i >= 0; i--) {
            Character c = chars.get(i);
            sb.append(c);
        }
        return sb.toString();
    }
}
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