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104. Maximum Depth of Binary Tree

Problem Description

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

Note: A leaf is a node with no children.

Detail instruction can be found here.

Example:

    3
   / \
  9  20
    /  \
   15   7

return 3

Solution

Approach 1: Recursive

private int ans;
public int maxDepth(TreeNode root) {
    ans = 0;
    maxDepth(root, 1);
    return ans;
}

private void maxDepth(TreeNode root, int depth) {
    if (root == null)   return;
    ans = Math.max(ans, depth);
    maxDepth(root.left, depth + 1);
    maxDepth(root.right, depth + 1);
}

Approach 2: Recursive

public int maxDepth(TreeNode root) {
    if (root == null)   return 0;
    return 1 + Math.max(maxDepth(root.left), maxDepth(root.right));
}

Definition for a binary tree node.

public class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;
    TreeNode(int x) { val = x; }
}

Test

Compile with javac Solution.java and run with java Solution.

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