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.
这道题我用的BFS做，要求根到叶节点最短深度，我首先就想到了BFS并分层遍历。只要找到第一个叶节点就停止搜索返回已经搜索的层次就可以。
/**
* 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) {
if (root == null){
return 0;
}
Queue<TreeNode> queue = new LinkedList<>();
queue.offer(root);
int level = 0;
while (!queue.isEmpty()){
int size = queue.size();
level++;
for (int i = 0; i < size; i++){
TreeNode curt = queue.poll();
if (curt.left == null && curt.right == null){
return level;
}
if (curt.left != null){
queue.offer(curt.left);
}
if (curt.right != null){
queue.offer(curt.right);
}
}
}
return level;
}
}
