gist for leetcode 543

diameterOfBinaryTree.cpp

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int ans = 0;
    int diameterOfBinaryTree(TreeNode* root) {
        dfs(root);
        return ans;
    }
    
    int dfs(TreeNode *root) {
        if(!root) {
            return 0;
        }
        
        int leftDepth  = dfs(root->left);
        int rightDepth = dfs(root->right);
        
        //>> calcualte the max depth
        ans = max(ans, leftDepth + rightDepth);
        
        //>> return depth
        return max(leftDepth, rightDepth) + 1;
    }
};