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Leetcode 1827. Minimum Operations to Make the Array Increasing

Problem Statement

Given an array of integers nums (0-indexed), you are required to make the array strictly increasing. An array nums is strictly increasing if nums[i] < nums[i+1] for every 0 <= i < nums.length - 1. Return the minimum number of operations needed to make nums strictly increasing.

In one operation, you can increment an element of the array by 1.

Clarifying Questions

  1. Input size constraints: What is the maximum length of the array nums?
    • The length of the array can be up to 10^4.
  2. Element value constraints: What are the possible value ranges for the elements in nums?
    • Elements of the array can be in the range 0 <= nums[i] <= 10^4.
  3. Output requirements: Do we need to return anything specific other than the minimum number of operations?
    • Just return the minimum number of operations required.

Strategy

  1. Traverse through the array starting from the second element.
  2. For each element, check if the current element is less than or equal to the previous element (i.e., nums[i] <= nums[i-1]).
  3. If so, calculate the difference and increment the current element to nums[i-1] + 1. This will ensure the array remains strictly increasing.
  4. Count the number of operations needed to make all necessary increments.
  5. Continue the process for all elements in the array.
  6. Return the total count of operations.

Code

#include <vector>

class Solution {
public:
    int minOperations(std::vector<int>& nums) {
        int operations = 0;
        for (size_t i = 1; i < nums.size(); ++i) {
            if (nums[i] <= nums[i - 1]) {
                // The number of increments needed
                int increment = nums[i - 1] - nums[i] + 1;
                nums[i] += increment;
                operations += increment;
            }
        }
        return operations;
    }
};

Time Complexity

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