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.
/**
* Definition for a binary tree node.
* public class TreeNode {
* public int val;
* public TreeNode left;
* public TreeNode right;
* public TreeNode(int val=0, TreeNode left=null, TreeNode right=null) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
public class Solution {
public int MinDepth(TreeNode root) {
if(root == null){
return 0;
}
if(root.left == null && root.right == null){
return 1;
}
int left = int.MaxValue;
int right = int.MaxValue;
if(root.left != null){
left = MinDepth(root.left);
}
if(root.right != null){
right = MinDepth(root.right);
}
return 1+ Math.Min(left, right);
}
}Time Complexity: O(n)
Space Complexity: O(1)
