g0201_0300.s0222_count_complete_tree_nodes.Solution Maven / Gradle / Ivy

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Java-based LeetCode algorithm problem solutions, regularly updated

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package g0201_0300.s0222_count_complete_tree_nodes;

// #Easy #Depth_First_Search #Tree #Binary_Search #Binary_Tree #Binary_Search_II_Day_10
// #2022_07_04_Time_0_ms_(100.00%)_Space_50_MB_(37.43%)

import com_github_leetcode.TreeNode;

/*
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
public class Solution {
    public int countNodes(TreeNode root) {
        if (root == null) {
            return 0;
        }
        int leftHeight = leftHeight(root);
        int rightHeight = rightHeight(root);
        // case 1: When Height(Left sub-tree) = Height(right sub-tree) 2^h - 1
        if (leftHeight == rightHeight) {
            return (1 << leftHeight) - 1;
        } else {
            return 1 + countNodes(root.left) + countNodes(root.right);
        }
    }

    private int leftHeight(TreeNode root) {
        if (root == null) {
            return 0;
        }
        return 1 + leftHeight(root.left);
    }

    private int rightHeight(TreeNode root) {
        if (root == null) {
            return 0;
        }
        return 1 + rightHeight(root.right);
    }
}