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.

递归：

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     int minDepth(TreeNode* root) {
13         if(root == NULL)
14             return 0;
15         if(root->left == NULL && root->right == NULL)
16             return 1;
17         if(root->left == NULL && root->right != NULL)
18             return minDepth(root->right) + 1;
19         if(root->left != NULL && root->right == NULL)
20             return minDepth(root->left) + 1;
21         else
22             return min(minDepth(root->left), minDepth(root->right)) + 1;
23         // if(root == NULL)
24         //     return 0;
25         // int l = minDepth(root->left);
26         // int r = minDepth(root->right);
27         // if(l == 0)
28         //     return r + 1;
29         // if(r == 0)
30         //     return l + 1;
31         // return (l < r ? l : r) + 1;
32     }
33 };

bfs：

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     int minDepth(TreeNode* root) {
13         if(root == NULL)
14             return 0;
15         int num = 0;
16         queue<TreeNode*> q;
17         TreeNode* temp;
18         q.push(root);
19         while(!q.empty()){
20             num++;
21             int len = q.size();
22             while(len--){
23                 temp = q.front();
24                 q.pop();
25                 if(temp->left == NULL && temp->right == NULL)
26                     return num;
27                 if(temp->left != NULL)
28                     q.push(temp->left);
29                 if(temp->right != NULL)
30                     q.push(temp->right);
31             }
32         }
33     }
34 };

 

posted @ 2017-02-18 16:26  琴影  阅读(202)  评论(0)  编辑  收藏  举报