title: Minimum Depth of Binary Tree
tags:
- minimum-depth-of-binary-tree
- No.111
- simple
- tree
- breadth-first-search
Description
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.
Corner Cases
- empty root
Solutions
Layer-First Traverse
Apply BFS, return when there is a leaf node.
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public int minDepth(TreeNode root) {
Queue<TreeNode> que = new LinkedList<TreeNode>();
if (root == null) {return 0;}
que.offer(root);
int curr = 0;
int nlay = 1;
int dept = 1;
while (!que.isEmpty()) {
nlay = que.size();
curr = 0;
while(curr < nlay) {
TreeNode x = que.poll();
if (x.left == null && x.right == null) {return dept;}
if (x.left != null) {que.offer(x.left);}
if (x.right != null) {que.offer(x.right);}
curr = curr + 1;
}
dept = dept + 1;
}
return dept;
}
}
