title
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.
注意：叶子节点是左右孩子都为空的节点
solution
思路：
- 递归，若为空树返回0；
- 若左子树为空，则返回右子树的最小深度+1；（加1是因为要加上根这一层，下同）
- 若右子树为空，则返回左子树的最小深度+1；
- 若左右子树均不为空，则取左、右子树最小深度的较小值，+1；
/**
* Definition for binary tree
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
int depth(TreeNode root){
if(root==null){
return 0;
}
if(root.left==null)
return depth(root.right)+1;
else if(root.right==null)
return depth(root.left)+1;
else{
int left=depth(root.left);
int right=depth(root.right);
// return left<right?left+1:right+1;
return Math.min(left,right)+1;
}
}
public int run(TreeNode root) {
return depth(root);
}
}