Minimum Depth of Binary Tree LeetCode solution in Java

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/**
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 * Definition for a binary tree node. public class TreeNode { int val; TreeNode left; TreeNode
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 * right; TreeNode() {} TreeNode(int val) { this.val = val; } TreeNode(int val, TreeNode left,
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 * TreeNode right) { this.val = val; this.left = left; this.right = right; } }
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 */
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class Solution {
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  public int minDepth(TreeNode root) {
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    if (root == null) return 0;
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    int left = minDepth(root.left);
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    int right = minDepth(root.right);
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    if (root.left == null) return right + 1;
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    if (root.right == null) return left + 1;
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    return Math.min(left, right) + 1;
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  }
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}