Today I have done Search in a Binary Search Tree and leetcode's June LeetCoding Challenge with cpp.

Search in a Binary Search Tree

Description

You are given the root of a binary search tree (BST) and an integer val.

Find the node in the BST that the node's value equals val and return the subtree rooted with that node. If such a node does not exist, return null.

Example 1:

Input: root = [4,2,7,1,3], val = 2
Output: [2,1,3]

Example 2:

Input: root = [4,2,7,1,3], val = 5
Output: []

Constraints:

• The number of nodes in the tree is in the range [1, 5000].
• 1 <= Node.val <= 10^7
• root is a binary search tree.
• 1 <= val <= 10^7

Solution

class Solution {
public:
  TreeNode* searchBST(TreeNode* root, int val) {
    if(!root) return nullptr;
    if(root->val == val) return root;
    if(root->val < val) return searchBST(root->right, val);
    return searchBST(root->left, val);
  }
};

June LeetCoding Challenge 15

Description

Matchsticks to Square

You are given an integer array matchsticks where matchsticks[i] is the length of the ith matchstick. You want to use all the matchsticks to make one square. You should not break any stick, but you can link them up, and each matchstick must be used exactly one time.

Return true if you can make this square and false otherwise.

Example 1:

Input: matchsticks = [1,1,2,2,2]
Output: true
Explanation: You can form a square with length 2, one side of the square came two sticks with length 1.

Example 2:

Input: matchsticks = [3,3,3,3,4]
Output: false
Explanation: You cannot find a way to form a square with all the matchsticks.

Constraints:

• 1 <= matchsticks.length <= 15
• 0 <= matchsticks[i] <= 10^9

Solution

class Solution {
  vector<bool> used;
  int len;
  long long target;
  bool solve(vector<int> &m, int a, int b, int c, int d, int l) {
    if(l == len && a == target && b == target && c == target && d == target) {
      return true;
    }
    if(a > target || b > target || c > target || d > target) {
      return false;
    }
    if(solve(m, a + m[l], b, c, d, l + 1)) return true;
    if(solve(m, a, b + m[l], c, d, l + 1)) return true;
    if(solve(m, a, b, c + m[l], d, l + 1)) return true;
    return solve(m, a, b, c, d + m[l], l + 1);
  }
public:
  bool makesquare(vector<int>& matchsticks) {
    len = matchsticks.size();
    if(len < 4) return false;
    sort(matchsticks.rbegin(), matchsticks.rend());
    long long sum = 0;
    for(auto l : matchsticks) sum += l;
    if(sum % 4 || matchsticks.back() > sum / 4) return false;
    target = sum / 4;
    return solve(matchsticks, 0, 0, 0, 0, 0); 
  }
};