111Minimum Depth of Binary Tree – Easy¶
Problem:¶
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.
Thoughts:¶
This is a very typical BFS problem. It could also be solved by a DFS as well.
BFS has a better average performance on this problem.
Solutions:¶
/**
* Definition for binary tree
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public int minDepth(TreeNode root) {
if (root == null) {
return 0;
}
Queue<TreeNode> q = new LinkedList<TreeNode>();
q.add(root);
int count = 0;
while (q.size() > 0) {
int n = q.size();
count ++;
boolean end = false;
for (int i = 0; i < n; i ++) {
TreeNode node = q.remove();
if (node.left == null && node.right == null) {
end = true;
}
if (node.left != null) {
q.add(node.left);
}
if (node.right != null) {
q.add(node.right);
}
}
if (end == true) {
break;
}
}
return count;
}
}