g0501_0600.s0546_remove_boxes.Solution Maven / Gradle / Ivy

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Java-based LeetCode algorithm problem solutions, regularly updated

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package g0501_0600.s0546_remove_boxes;

// #Hard #Array #Dynamic_Programming #Memoization
// #2022_08_02_Time_45_ms_(95.58%)_Space_52.3_MB_(87.17%)

/**
 * 546 - Remove Boxes\.
 *
 * Hard
 *
 * You are given several `boxes` with different colors represented by different positive numbers.
 *
 * You may experience several rounds to remove boxes until there is no box left. Each time you can choose some continuous boxes with the same color (i.e., composed of `k` boxes, `k >= 1`), remove them and get `k * k` points.
 *
 * Return _the maximum points you can get_.
 *
 * **Example 1:**
 *
 * **Input:** boxes = [1,3,2,2,2,3,4,3,1]
 *
 * **Output:** 23
 *
 * **Explanation:**
 *
 *     [1, 3, 2, 2, 2, 3, 4, 3, 1] ----> [1, 3, 3, 4, 3, 1]
 *     (3\*3=9 points) ----> [1, 3, 3, 3, 1]
 *     (1\*1=1 points) ----> [1, 1]
 *     (3\*3=9 points) ----> []
 *     (2\*2=4 points)
 *
 * **Example 2:**
 *
 * **Input:** boxes = [1,1,1]
 *
 * **Output:** 9
 *
 * **Example 3:**
 *
 * **Input:** boxes = [1]
 *
 * **Output:** 1
 *
 * **Constraints:**
 *
 * *   `1 <= boxes.length <= 100`
 * *   `1 <= boxes[i] <= 100`
**/
public class Solution {
    private Integer[][][] dp;

    public int removeBoxes(int[] boxes) {
        int n = boxes.length;
        dp = new Integer[n][n][n + 1];
        return helper(boxes, 0, n - 1, 0);
    }

    private int helper(int[] boxes, int left, int right, int count) {
        if (left > right) {
            return 0;
        }
        if (dp[left][right][count] != null) {
            return dp[left][right][count];
        }
        int leftDash = left;
        int countDash = count;
        while (leftDash < right && boxes[leftDash] == boxes[leftDash + 1]) {
            leftDash++;
            countDash++;
        }
        int ans;
        ans = helper(boxes, leftDash + 1, right, 0) + (countDash + 1) * (countDash + 1);
        for (int i = leftDash + 1; i <= right; i++) {
            if (boxes[i] == boxes[leftDash]) {
                int temp =
                        helper(boxes, leftDash + 1, i - 1, 0)
                                + helper(boxes, i, right, countDash + 1);
                ans = Math.max(temp, ans);
            }
        }
        dp[left][right][count] = ans;
        return ans;
    }
}