LeetCode 1827. Minimum Operations to Make the Array Increasing

Description

https://leetcode.com/problems/minimum-operations-to-make-the-array-increasing/

You are given an integer array nums (0-indexed). In one operation, you can choose an element of the array and increment it by 1.

  • For example, if nums = [1,2,3], you can choose to increment nums[1] to make nums = [1,3,3].

Return the minimum number of operations needed to make nums strictly increasing.

An array nums is strictly increasing if nums[i] < nums[i+1] for all 0 <= i < nums.length - 1. An array of length 1 is trivially strictly increasing.

Example 1:

Input: nums = [1,1,1]
Output: 3
Explanation: You can do the following operations:
1) Increment nums[2], so nums becomes [1,1,2].
2) Increment nums[1], so nums becomes [1,2,2].
3) Increment nums[2], so nums becomes [1,2,3].

Example 2:

Input: nums = [1,5,2,4,1]
Output: 14

Example 3:

Input: nums = [8]
Output: 0

Constraints:

  • 1 <= nums.length <= 5000
  • 1 <= nums[i] <= 104

Explanation

Iterate the list and whenever find a number is no greater than the previous one, increase that number and count the operations.

Python Solution

class Solution:
    def minOperations(self, nums: List[int]) -> int:
        
        count = 0
        
        if len(nums) < 2:
            return count
        
        
        prev = None
        for i, num in enumerate(nums):
            if prev and num <= prev:
                count += prev - num + 1
                nums[i] = prev + 1
            prev = nums[i]
        
        
        return count
            
  • Time Complexity: O(N).
  • Space Complexity: O(1).

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