11. Minimum Depth of Binary Tree 11.二叉树的最小深度
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.
Note: A leaf is a node with no children.
Example:
Given binary tree [3,9,20,null,null,15,7]
,
3
/ \
9 20
/ \
15 7
return its minimum depth = 2.
复习时还不会的地方:左右都不为空的时候,min也要+1,因为长度也在增加
结果2 = 左边加1得出来的。
如果是最小值并且一边为空的话,就是0 + 1了,这是不准确的,因为没路的一边其实没用。其实是非空的一侧才长度增加
概括是:有路就找最短,没路就找有路的。这是和最大长度的一个区别。
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
public int minDepth(TreeNode root) {
//cc
if (root == null)
return 0;
int left = minDepth(root.left);
int right = minDepth(root.right);
int min = Math.min(left, right);
if (left == 0) {
return right + 1;
}else if (right == 0) {
return left + 1;
}else
return min + 1;
}
}