LeetCode OJ:Minimum Depth of Binary Tree

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.
アルゴリズムの思想:層順に遍歴して、最初の葉のノードを見つけます

/**
 * 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) {
        if(!root)return 0;  
        queue<TreeNode *>que;
        int minLen=0;  
        int curLev=1;  
        int nextLev=0;  
        int depth=0;
        que.push(root);  
        while(!que.empty()){  
            TreeNode *cur=que.front();  
            que.pop();  
            if(cur->left==NULL&&cur->right==NULL){
                return depth+1;
            }
            if(cur->left){que.push(cur->left);nextLev++;}  
            if(cur->right){que.push(cur->right);nextLev++;}  
            if(--curLev==0){  
                curLev=nextLev;  
                nextLev=0; 
                depth++;
            }  
        }  
    }
};

再帰版

/**
 * 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) {
        return minDepth(root,false);
    }
private:
    static int minDepth(const TreeNode *root,bool hasbrother){
        if(!root)return hasbrother?INT_MAX:0;
        return 1+min(minDepth(root->left,root->right),
                minDepth(root->right,root->left));
    }
};