算法作业_37(2017.6.19第十八周)

104. 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.

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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.

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解析：这是两道相似的二叉树递归问题，但是测试用例还是存在一些差别。如111最小的长度，如果一棵树只有一颗子树，那么最短长度不是0 也不是1，而是子数的最短长度。

Maximum Depth of Binary Tree：

/** * 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 maxDepth(TreeNode* root) {        if(root == NULL) return 0;        int leftMax = maxDepth(root->left);        int rightMax = maxDepth(root->right);        return max( leftMax , rightMax) +1;    }};

Minimum Depth of Binary Tree

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