LeetCode 111. Minimum Depth of Binary Tree

111. Minimum Depth of Binary Tree

Difficulty:: Easy

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.

Solution

Language: Java

/**
 * 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;
           }
            if (root.left == null && root.right == null) {
                  return 1;
           }
            if (root.left == null) {
                  return minDepth(root.right) + 1;
           }
            if (root.right == null) {
                  return minDepth(root.left) + 1;
           }
            return Math.min(minDepth(root.left), minDepth(root.right)) + 1;
     }
}