g0601_0700.s0654_maximum_binary_tree.Solution Maven / Gradle / Ivy

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Java-based LeetCode algorithm problem solutions, regularly updated

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package g0601_0700.s0654_maximum_binary_tree;

// #Medium #Array #Tree #Binary_Tree #Stack #Monotonic_Stack #Divide_and_Conquer
// #2022_03_21_Time_3_ms_(84.36%)_Space_54.4_MB_(17.04%)

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 TreeNode constructMaximumBinaryTree(int[] nums) {
        return mbt(nums, 0, nums.length - 1);
    }

    private TreeNode mbt(int[] nums, int l, int r) {
        if (l > r || l >= nums.length || r < 0) {
            return null;
        }
        if (l == r) {
            return new TreeNode(nums[r]);
        }
        int max = Integer.MIN_VALUE;
        int maxidx = 0;
        for (int i = l; i <= r; i++) {
            if (nums[i] > max) {
                max = nums[i];
                maxidx = i;
            }
        }
        TreeNode root = new TreeNode(max);
        root.left = (mbt(nums, l, maxidx - 1));
        root.right = (mbt(nums, maxidx + 1, r));
        return root;
    }
}