g0901_1000.s0962_maximum_width_ramp.Solution Maven / Gradle / Ivy

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Java-based LeetCode algorithm problem solutions, regularly updated

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package g0901_1000.s0962_maximum_width_ramp;

// #Medium #Array #Stack #Monotonic_Stack #2022_03_31_Time_6_ms_(90.69%)_Space_57.6_MB_(36.44%)

/**
 * 962 - Maximum Width Ramp\.
 *
 * Medium
 *
 * A **ramp** in an integer array `nums` is a pair `(i, j)` for which `i < j` and `nums[i] <= nums[j]`. The **width** of such a ramp is `j - i`.
 *
 * Given an integer array `nums`, return _the maximum width of a **ramp** in_ `nums`. If there is no **ramp** in `nums`, return `0`.
 *
 * **Example 1:**
 *
 * **Input:** nums = [6,0,8,2,1,5]
 *
 * **Output:** 4
 *
 * **Explanation:** The maximum width ramp is achieved at (i, j) = (1, 5): nums[1] = 0 and nums[5] = 5.
 *
 * **Example 2:**
 *
 * **Input:** nums = [9,8,1,0,1,9,4,0,4,1]
 *
 * **Output:** 7
 *
 * **Explanation:** The maximum width ramp is achieved at (i, j) = (2, 9): nums[2] = 1 and nums[9] = 1.
 *
 * **Constraints:**
 *
 * *   2 <= nums.length <= 5 * 10⁴
 * *   0 <= nums[i] <= 5 * 10⁴
**/
public class Solution {
    public int maxWidthRamp(int[] nums) {
        int m = nums.length;
        int[] dp = new int[m];
        int minInd = 0;
        int ramp = 0;
        for (int i = 0; i < m; i++) {
            int prInd = minInd;
            while (prInd > 0 && nums[i] >= nums[dp[prInd]]) {
                prInd = dp[prInd];
            }
            dp[i] = prInd;
            if (nums[i] >= nums[prInd]) {
                ramp = Math.max(ramp, i - prInd);
            }
            minInd = nums[i] < nums[minInd] ? i : minInd;
        }
        return ramp;
    }
}