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  • LeetCode 23. Merge k Sorted Lists
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  • LeetCode 25. Reverse Nodes in k-Group
  • LeetCode 26. Remove Duplicates from Sorted Array
  • LeetCode 27. Remove Element
  • LeetCode 28. Implement strStr()
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  • LeetCode 30. Substring with Concatenation of All Words
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  • LeetCode 42. Trapping Rain Water
  • LeetCode 56. Merge Intervals
  • LeetCode 67. Add Binary
  • LeetCode 81. Search in Rotated Sorted Array II
  • LeetCode 124. Binary Tree Maximum Path Sum
  • LeetCode 125. Valid Palindrome
  • LeetCode 153. Find Minimum in Rotated Sorted Array
  • LeetCode 154. Find Minimum in Rotated Sorted Array II
  • LeetCode 157. Read N Characters Given Read4
  • LeetCode 158. Read N Characters Given Read4 II - Call multiple times
  • LeetCode 236. Lowest Common Ancestor of a Binary Tree
  • LeetCode 238. Product of Array Except Self
  • LeetCode 269. Alien Dictionary
  • Leetcode 295. Find Median from Data Stream
  • Leetcode 297. Serialize and Deserialize Binary Tree
  • LeetCode 300. Longest Increasing Subsequence
  • LeetCode 301. Remove Invalid Parentheses
  • LeetCode 336. Palindrome Pairs
  • LeetCode 407. Trapping Rain Water II
  • LeetCode 415. Add Strings
  • LeetCode 426. Convert Binary Search Tree to Sorted Doubly Linked List
  • LeetCode 489. Robot Room Cleaner
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  • LeetCode 1249. Minimum Remove to Make Valid Parentheses
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  • LeetCode 1644. Lowest Common Ancestor of a Binary Tree II
  • LeetCode 1650. Lowest Common Ancestor of a Binary Tree III
  • LeetCode 1676. Lowest Common Ancestor of a Binary Tree IV
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  • LeetCode 1751. Maximum Number of Events That Can Be Attended II
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  • LeetCode 1755. Closest Subsequence Sum
  • LeetCode 1760. Minimum Limit of Balls in a Bag
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  • LeetCode. 1775 Equal Sum Arrays With Minimum Number of Operations
  • LeetCode 1776. Car Fleet II
  • LeetCode 1778. Shortest Path in a Hidden Grid
  • LeetCode 1779. Find Nearest Point That Has the Same X or Y Coordinate
  • LeetCode 1780. Check if Number is a Sum of Powers of Three
  • LeetCode 1781. Sum of Beauty of All Substrings
  • LeetCode 1782. Count Pairs Of Nodes
  • LeetCode 1784. Check if Binary String Has at Most One Segment of Ones
  • LeetCode 1785. Minimum Elements to Add to Form a Given Sum
  • LeetCode 1786. Number of Restricted Paths From First to Last Node
  • LeetCode 1787. Make the XOR of All Segments Equal to Zero
  • LeetCode 1788. Maximize the Beauty of the Garden
  • LeetCode 1790. Check if One String Swap Can Make Strings Equal
  • LeetCode 1791. Find Center of Star Graph
  • LeetCode 1792. Maximum Average Pass Ratio
  • LeetCode 1793. Maximum Score of a Good Subarray
  • LeetCode 1794. Count Pairs of Equal Substrings With Minimum Difference
  • LeetCode 1796. Second Largest Digit in a String
  • LeetCode 1797. Design Authentication Manager
  • LeetCode 1798. Maximum Number of Consecutive Values You Can Make
  • LeetCode 1799. Maximize Score After N Operations
  • LeetCode 1800. Maximum Ascending Subarray Sum
  • LeetCode 1801. Number of Orders in the Backlog
  • LeetCode 1802. Maximum Value at a Given Index in a Bounded Array
  • LeetCode 1803. Count Pairs With XOR in a Range
  • LeetCode 1804. Implement Trie II (Prefix Tree)
  • LeetCode 1805. Number of Different Integers in a String
  • LeetCode 1807. Evaluate the Bracket Pairs of a String
  • LeetCode 1808. Maximize Number of Nice Divisors
  • LeetCode 1810. Minimum Path Cost in a Hidden Grid
  • LeetCode 1812. Determine Color of a Chessboard Square
  • LeetCode 1813. Sentence Similarity III
  • LeetCode 1814. Count Nice Pairs in an Array
  • LeetCode 1815. Maximum Number of Groups Getting Fresh Donuts
  • LeetCode 1816. Truncate Sentence
  • LeetCode 1817. Finding the Users Active Minutes
  • LeetCode 1818. Minimum Absolute Sum Difference
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  • LeetCode 1820. Maximum Number of Accepted Invitations
  • LeetCode 1822. Sign of the Product of an Array
  • LeetCode 1824. Minimum Sideway Jumps
  • LeetCode 1825. Finding MK Average
  • LeetCode 1826. Faulty Sensor
  • LeetCode 1827. Minimum Operations to Make the Array Increasing
  • LeetCode 1828. Queries on Number of Points Inside a Circle
  • LeetCode 1829. Maximum XOR for Each Query
  • LeetCode 1830. Minimum Number of Operations to Make String Sorted
  • LeetCode 1832. Check if the Sentence Is Pangram
  • LeetCode 1833. Maximum Ice Cream Bars
  • LeetCode 1834. Single-Threaded CPU
  • LeetCode 1835. Find XOR Sum of All Pairs Bitwise AND
  • LeetCode 1836. Remove Duplicates From an Unsorted Linked List
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  • LeetCode 1839. Longest Substring Of All Vowels in Order
  • LeetCode 1840. Maximum Building Height
  • LeetCode 1847. Closest Room
  • LeetCode 1850. Minimum Adjacent Swaps to Reach the Kth Smallest Number
  • LeetCode 1851. Minimum Interval to Include Each Query
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LeetCode 1803. Count Pairs With XOR in a Range

Trie

Given a (0-indexed) integer array nums and two integers low and high, return the number of nice pairs.

A nice pair is a pair (i, j) where 0 <= i < j < nums.length and low <= (nums[i] XOR nums[j]) <= high.

Example 1:

Input: nums = [1,4,2,7], low = 2, high = 6
Output: 6
Explanation: All nice pairs (i, j) are as follows:
    - (0, 1): nums[0] XOR nums[1] = 5 
    - (0, 2): nums[0] XOR nums[2] = 3
    - (0, 3): nums[0] XOR nums[3] = 6
    - (1, 2): nums[1] XOR nums[2] = 6
    - (1, 3): nums[1] XOR nums[3] = 3
    - (2, 3): nums[2] XOR nums[3] = 5

Example 2:

Input: nums = [9,8,4,2,1], low = 5, high = 14
Output: 8
Explanation: All nice pairs (i, j) are as follows:
​​​​​    - (0, 2): nums[0] XOR nums[2] = 13
    - (0, 3): nums[0] XOR nums[3] = 11
    - (0, 4): nums[0] XOR nums[4] = 8
    - (1, 2): nums[1] XOR nums[2] = 12
    - (1, 3): nums[1] XOR nums[3] = 10
    - (1, 4): nums[1] XOR nums[4] = 9
    - (2, 3): nums[2] XOR nums[3] = 6
    - (2, 4): nums[2] XOR nums[4] = 5

Constraints:

  • 1 <= nums.length <= 2 * 104

  • 1 <= nums[i] <= 2 * 104

  • 1 <= low <= high <= 2 * 104

Solution

class Solution {
    
    const int HEIGHT = 14;
    
    class TreeNode {
    public:
        TreeNode* next[2];
        int cnt;
        TreeNode () {
            next[0] = nullptr;
            next[1] = nullptr;
            cnt = 0;
        };
    };
    
    void insert(TreeNode* root, int num) {
        TreeNode* cur = root;
        for (int j = HEIGHT; j >= 0; j--) {
            int index = ((num >> j) & 1);
            if (cur->next[index] == nullptr)
                cur->next[index] = new TreeNode();
            cur = cur->next[index];
            cur->cnt++;
        }
    }
    
    int GetCount(TreeNode* root, int num, int limit) {
        TreeNode* cur = root;
        int cnt = 0;
        for (int j = HEIGHT; j >= 0; j--) {
            int bit_num = ((num >> j) & 1);
            int bit_limit = ((limit >> j) & 1);
            
            if (bit_limit == 1) {
                // For bit_num branch, its values are all < limit
                if (cur->next[bit_num] != nullptr) {
                    cnt += cur->next[bit_num]->cnt;
                }
                // we try to pick the side so that it XOR bit_num is 1.
                cur = cur->next[1 - bit_num];
            } else {
                // we pick 'bit_num' child so that it does not exceed limit.
                cur = cur->next[bit_num];
            }
            
            if (cur == nullptr) break;
        }
        return cnt;
    }
    
public:
    int countPairs(vector<int>& nums, int low, int high) {
        TreeNode* root = new TreeNode();
        
        int ans = 0;
        for (int num : nums) {
            ans += GetCount(root, num, high + 1) - GetCount(root, num, low);
            insert(root, num);
        }
        
        return ans;
    }
};
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