[LeetCode 解题报告]111. Minimum Depth of Binary Tree

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:

Given binary tree [3,9,20,null,null,15,7],

    3
   / \
  9  20
    /  \
   15   7

return its minimum depth = 2.

考察：二叉树最小深度； 

/**
 * 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 minDepth(TreeNode* root) {
        if (root == NULL)
            return 0;
        if (root->left == NULL && root->right == NULL)
            return 1;
        
        if (root->left == NULL)
            return minDepth(root->right) + 1;
        else if (root->right == NULL)
            return minDepth(root->left) + 1;
        else
            return min(minDepth(root->left), minDepth(root->right)) + 1;
    }
};