Minimum(Maximum) Depth of Binary Tree

题目一：计算最小深度（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.

此题与计算二叉树的高度或深度不同，他是到最高叶子节点的路径长度，是最大深度。

具体实现

我们知道，除了根节点之外，左右指针都为空的节点是叶子节点。

即  if(left==0 && right==0) return 1;

而当其中一个子指针为空时，叶子节点在另一个非空的子指针上，故有 if(left==0 && right!=0) return 1+right;     if(left!=0 && right==0) return 1+left;

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {  public:      int minDepth(TreeNode *root) {          // Start typing your C/C++ solution below           // DO NOT write int main() function           if(!root) return 0;                    int left = minDepth( root->left);          int right = minDepth( root->right);          if(left==0 && right!=0)            return 1+right;        if(left!=0 && right==0)             return 1+left;        if(left && right)             return 1 + min(left, right);          if(left==0 && right==0)            return 1;     }  };  

题目二：计算最大深度（Maximum Depth of Binary Tree）

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    int maxDepth(TreeNode *root) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        if(!root)            return 0;        int left = maxDepth(root->left);        int right = maxDepth(root->right);        if(left==0)            return 1+right;        if(right==0)            return 1+left;        return 1+max(left,right);            }};

其他代码：

class Solution {  public:      int minDepth(TreeNode *root) {          // Start typing your C/C++ solution below           // DO NOT write int main() function           if(!root) return 0;                    int left = minDepth( root->left);          int right = minDepth( root->right);          return (left>right)?(1+left):(1+right);    }  };