第十八周：[Leetcode]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.

---

和求最大距离不一样，因为是求到叶子节点的最小距离，需要区分左右子树有可能为空的情况。

---

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 && root -> right == NULL)            return minDepth(root -> left) + 1;        if(root -> left == NULL && root -> right != NULL)            return minDepth(root -> right) + 1;        return min(minDepth(root -> left) + 1,minDepth(root -> right) + 1);    }};