【LeetCode】111. Minimum Depth of Binary Tree

题目：

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.

提示：

这道题用BFS或者DFS都可以。

代码：

DFS：

/**
 * 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) return 0;
        if(!root->left) return 1 + minDepth(root->right);
        if(!root->right) return 1 + minDepth(root->left);
        return 1+min(minDepth(root->left),minDepth(root->right));
    }
};

BFS：

/**
 * 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) {
        int depth = 0;
        if (root == NULL) return depth;
        queue<TreeNode*> q;
        q.push(root); ++depth;
        
        while (!q.empty()) {
            TreeNode* node;
            int size = q.size();
            for (int i = 0; i < size; ++i) {
                node = q.front(); q.pop();
                if (!node->left && !node->right) return depth;
                if (node->left) q.push(node->left);
                if (node->right) q.push(node->right);
            }
            ++depth;
        }
    }
};