Today I have done leetcode's April LeetCoding Challenge with cpp.

April LeetCoding Challenge 4

Description

Lowest Common Ancestor of Deepest Leaves

Given the root of a binary tree, return the lowest common ancestor of its deepest leaves.

Recall that:

• The node of a binary tree is a leaf if and only if it has no children
• The depth of the root of the tree is 0. if the depth of a node is d, the depth of each of its children is d + 1.
• The lowest common ancestor of a set S of nodes, is the node A with the largest depth such that every node in S is in the subtree with root A.

Example 1:

Input: root = [3,5,1,6,2,0,8,null,null,7,4]
Output: [2,7,4]
Explanation: We return the node with value 2, colored in yellow in the diagram.
The nodes coloured in blue are the deepest leaf-nodes of the tree.
Note that nodes 6, 0, and 8 are also leaf nodes, but the depth of them is 2, but the depth of nodes 7 and 4 is 3.

Example 2:

Input: root = [1]
Output: [1]
Explanation: The root is the deepest node in the tree, and it's the lca of itself.

Example 3:

Input: root = [0,1,3,null,2]
Output: [2]
Explanation: The deepest leaf node in the tree is 2, the lca of one node is itself.

Constraints:

• The number of nodes in the tree will be in the range [1, 1000].
• 0 <= Node.val <= 1000
• The values of the nodes in the tree are unique.

Note: This question is the same as 865: https://leetcode.com/problems/smallest-subtree-with-all-the-deepest-nodes/

Solution

class Solution {
  int solve(TreeNode *&result, TreeNode *root, int level = 0) {
    if(!root) return 0;
    TreeNode *leftR = nullptr;
    TreeNode *rightR = nullptr;
    int left = solve(leftR, root->left, level + 1);
    int right = solve(rightR, root->right, level + 1);
    if(left > right) {
      result = leftR;
      return left;
    } else if(right > left) {
      result = rightR;
      return right;
    }
    result = root;
    return max(left, level);
  }
public:
  TreeNode* lcaDeepestLeaves(TreeNode* root) {
    TreeNode *answer;
    solve(answer, root, 0);
    return answer;
  }
};

// Accepted
// 81/81 cases passed (0 ms)
// Your runtime beats 100 % of cpp submissions
// Your memory usage beats 87.17 % of cpp submissions (22 MB)