Today I have done Make Two Arrays Equal by Reversing Sub-arrays on leetcode and leetcode's December LeetCoding Challenge with cpp.

Make Two Arrays Equal by Reversing Sub-arrays

Description

Given two integer arrays of equal length target and arr.

In one step, you can select any non-empty sub-array of arr and reverse it. You are allowed to make any number of steps.

Return True if you can make arr equal to target, or False otherwise.

Example 1:

Input: target = [1,2,3,4], arr = [2,4,1,3]
Output: true
Explanation: You can follow the next steps to convert arr to target:
1- Reverse sub-array [2,4,1], arr becomes [1,4,2,3]
2- Reverse sub-array [4,2], arr becomes [1,2,4,3]
3- Reverse sub-array [4,3], arr becomes [1,2,3,4]
There are multiple ways to convert arr to target, this is not the only way to do so.

Example 2:

Input: target = [7], arr = [7]
Output: true
Explanation: arr is equal to target without any reverses.

Example 3:

Input: target = [1,12], arr = [12,1]
Output: true

Example 4:

Input: target = [3,7,9], arr = [3,7,11]
Output: false
Explanation: arr doesn't have value 9 and it can never be converted to target.

Example 5:

Input: target = [1,1,1,1,1], arr = [1,1,1,1,1]
Output: true

Constraints:

• target.length == arr.length
• 1 <= target.length <= 1000
• 1 <= target[i] <= 1000
• 1 <= arr[i] <= 1000

Solution

use count

class Solution {
public:
    bool canBeEqual(vector<int>& target, vector<int>& arr) {
        int cnt[1001] = {0};
        for(auto i : target) {
            cnt[i] += 1;
        }
        for(auto i : arr) {
            cnt[i] -= 1;
        }
        for(int i = 0; i <= 1000; ++i) {
            if(cnt[i]) return false;
        }
        return true;
    }
};

or check if there are permutations of each other.

class Solution {
public:
    bool canBeEqual(vector<int>& target, vector<int>& arr) {
        sort(target.begin(), target.end());
        sort(arr.begin(), arr.end());
        return arr == target;
    }
};

December LeetCoding Challenge 22

Description

Balanced Binary Tree

Given a binary tree, determine if it is height-balanced.

For this problem, a height-balanced binary tree is defined as:

a binary tree in which the left and right subtrees of every node differ in height by no more than 1.

Example 1:

Input: root = [3,9,20,null,null,15,7]
Output: true

Example 2:

Input: root = [1,2,2,3,3,null,null,4,4]
Output: false

Example 3:

Input: root = []
Output: true

Constraints:

• The number of nodes in the tree is in the range [0, 5000].
• -104 <= Node.val <= 104

Solution

balanced binary tree is not balanced binary search tree

class Solution {
    pair<bool, int> getMinMax(TreeNode* root) {
        if(!root) return make_pair(true, 0);
        auto [balancedLeft, heightLeft] = getMinMax(root->left);
        auto [balancedRight, heightRight] = getMinMax(root->right);
        int diff = abs(heightLeft-heightRight);
        bool balanced = balancedLeft && balancedRight && diff < 2;
        return make_pair(balanced, 1+max(heightRight, heightLeft));
    }
public:
    bool isBalanced(TreeNode* root) {
        auto [balanced, _height] = getMinMax(root);
        return balanced;
    }
};