[leetcode #1413] Minimum Value to Get Positive Step by Step Sum

Problem

Given an array of integers nums, you start with an initial positive value startValue.

In each iteration, you calculate the step by step sum of startValue plus elements in nums (from left to right).

Return the minimum positive value of startValue such that the step by step sum is never less than 1.

Example 1:

Input: nums = [-3,2,-3,4,2]
Output: 5
Explanation: If you choose startValue = 4, in the third iteration your step by step sum is less than 1.
            step by step sum
            startValue = 4 | startValue = 5 | nums
              (4 -3 ) = 1  | (5 -3 ) = 2    |  -3
              (1 +2 ) = 3  | (2 +2 ) = 4    |   2
              (3 -3 ) = 0  | (4 -3 ) = 1    |  -3
              (0 +4 ) = 4  | (1 +4 ) = 5    |   4
              (4 +2 ) = 6  | (5 +2 ) = 7    |   2

Example 2:

Input: nums = [1,2]
Output: 1
Explanation: Minimum start value should be positive. 

Example 3:

Input: nums = [1,-2,-3]
Output: 5

Constraints:

・ 1 <= nums.length <= 100
・ -100 <= nums[i] <= 100

Idea

아주 쉬운 문제다.

주어진 array를 탐색하면서 Running Sum을 계산하면서 running sum이 최소가 되는 값을 저장한다.

마지막으로 최소값이 0보다 클경우는 1을 리턴하고, 그렇지 않을 경우 -1을 곱한 뒤 1을 더해주면 된다.

Solution

class Solution {
    public int minStartValue(int[] nums) {
        int min = Integer.MAX_VALUE;
        int sum = 0;

        for (int i=0; i < nums.length; i++) {
            sum += nums[i];
            if (sum < min) {
                min = sum;
            }
        }

        return min > 0 ? 1 : -min + 1;
    }
}

Reference

https://leetcode.com/problems/minimum-value-to-get-positive-step-by-step-sum/