[leetcode]111. Minimum Depth of Binary Tree

题目链接：https://leetcode.com/problems/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.

方法1：
class Solution{
public:
int minDepth(TreeNode * root)
{
if(root==NULL) return 0;
int mark=INT_MAX;

preTraverse(root, 1, mark);
return mark;
}

void preTraverse(TreeNode * root,int depth,int &mark)
{
if(root==NULL) return;
if(root->left==NULL && root->right==NULL)
{
if(depth<mark)
mark=depth;
}
preTraverse(root->left, depth+1,mark);
preTraverse(root->right, depth+1,mark);
}
};


方法2：
class Solution {
public:
int minDepth(TreeNode *root) {
if(root==NULL)
return 0;
int mleft=minDepth(root->left);
int mright=minDepth(root->right);
if(mleft==0)
return 1+mright;
else if(mright==0)
return 1+mleft;
else return min(mleft,mright)+1;
}
};