111.minimum-depth-of-binary-tree.cpp

/*
 * @lc app=leetcode id=111 lang=cpp
 *
 * [111] Minimum Depth of Binary Tree
 *
 * https://leetcode.com/problems/minimum-depth-of-binary-tree/description/
 *
 * algorithms
 * Easy (42.76%)
 * Likes:    4962
 * Dislikes: 1020
 * Total Accepted:    848.9K
 * Total Submissions: 2M
 * Testcase Example:  '[3,9,20,null,null,15,7]'
 *
 * Given a binary tree, find its minimum depth.
 * 
 * The minimum depth is the number of nodes along the shortest path from the
 * root node down to the nearest leaf node.
 * 
 * Note: A leaf is a node with no children.
 * 
 * 
 * Example 1:
 * 
 * 
 * Input: root = [3,9,20,null,null,15,7]
 * Output: 2
 * 
 * 
 * Example 2:
 * 
 * 
 * Input: root = [2,null,3,null,4,null,5,null,6]
 * Output: 5
 * 
 * 
 * 
 * Constraints:
 * 
 * 
 * The number of nodes in the tree is in the range [0, 10^5].
 * -1000 <= Node.val <= 1000
 * 
 * 
 */

// @lc code=start
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int minDepth(TreeNode* root) {
        if(!root) return 0;
        int L = minDepth(root->left),R = minDepth(root->right);
        return 1 + (min(L,R)?min(L,R):max(L,R));
    }
};
// @lc code=end