2289. Steps to Make Array Non-decreasing

Problem

You are given a 0-indexed integer array nums. In one step, remove all elements nums[i] where nums[i - 1] > nums[i] for all 0 < i < nums.length.

Return **the number of steps performed until *nums* becomes a non-decreasing array**.

  Example 1:

Input: nums = [5,3,4,4,7,3,6,11,8,5,11]
Output: 3
Explanation: The following are the steps performed:
- Step 1: [5,3,4,4,7,3,6,11,8,5,11] becomes [5,4,4,7,6,11,11]
- Step 2: [5,4,4,7,6,11,11] becomes [5,4,7,11,11]
- Step 3: [5,4,7,11,11] becomes [5,7,11,11]
[5,7,11,11] is a non-decreasing array. Therefore, we return 3.

Example 2:

Input: nums = [4,5,7,7,13]
Output: 0
Explanation: nums is already a non-decreasing array. Therefore, we return 0.

  Constraints:

• 1 <= nums.length <= 105

• 1 <= nums[i] <= 109

Solution

/**
 * @param {number[]} nums
 * @return {number}
 */
var totalSteps = function(nums) {
    var dp = Array(nums.length).fill(0);
    var stack = [];
    for (var i = nums.length - 1; i >= 0; i--) {
        while (stack.length && nums[i] > nums[stack[stack.length - 1]]) {
            dp[i] = Math.max(dp[i] + 1, dp[stack.pop()]);
        }
        stack.push(i);
    }
    return Math.max(...dp);
};

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).