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Leetcode111-minimumDepthOfBinaryTree

Posted on Edited on In Views: Valine:
Solution Report of LeetCode Acceptted

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],

1
2
3
4
5
  3
 / \
9  20
  /  \
 15   7

return its minimum depth = 2.

Solution

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/**
 * 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;
        return helper(root, 1);
    }
    private int helper(TreeNode node, int depth){
        if (node.left == null && node.right == null) return depth;
        if (node.left != null && node.right != null) 
            return Math.min(helper(node.left, depth + 1), helper(node.right, depth + 1));
        else if (node.left == null)
            return helper(node.right, depth + 1);
        else return helper(node.left, depth + 1);
    }
}