104. Maximum Depth of Binary Tree

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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.

Example:

Given binary tree [3,9,20,null,null,15,7],

    3
   / \
  9  20
    /  \
   15   7

return its depth = 3.

Solution

這題概念跟上一題一樣

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