1176. Diet Plan Performance.cpp

// ***
//
// A dieter consumes calories[i] calories on the i-th day.
//
// Given an integer k, for every consecutive sequence of k days (calories[i], calories[i+1], ..., calories[i+k-1] for
// all 0 <= i <= n-k), they look at T, the total calories consumed during that sequence of k days (calories[i] +
// calories[i+1] + ... + calories[i+k-1]):
//
// If T < lower, they performed poorly on their diet and lose 1 point;
// If T > upper, they performed well on their diet and gain 1 point;
// Otherwise, they performed normally and there is no change in points.
// Initially, the dieter has zero points. Return the total number of points the dieter has after dieting for
// calories.length days.
//
// Note that the total points can be negative.
//
//
// Example 1:
//
// Input: calories = [1,2,3,4,5], k = 1, lower = 3, upper = 3
// Output: 0
// Explanation: Since k = 1, we consider each element of the array separately and compare it to lower and upper.
// calories[0] and calories[1] are less than lower so 2 points are lost.
// calories[3] and calories[4] are greater than upper so 2 points are gained.
//
//
// Example 2:
//
// Input: calories = [3,2], k = 2, lower = 0, upper = 1
// Output: 1
// Explanation: Since k = 2, we consider subarrays of length 2.
// calories[0] + calories[1] > upper so 1 point is gained.
//
//
// Example 3:
//
// Input: calories = [6,5,0,0], k = 2, lower = 1, upper = 5
// Output: 0
// Explanation:
// calories[0] + calories[1] > upper so 1 point is gained.
// lower <= calories[1] + calories[2] <= upper so no change in points.
// calories[2] + calories[3] < lower so 1 point is lost.
//
// ***
//
// Just an easy boring sliding window quesiton.

class Solution {
public:
    int dietPlanPerformance(vector<int>& calories, int k, int lower, int upper) {
        int windowSum = 0, totalPoints = 0;
        int left = 0, right = 0;

        while (right < calories.size()) {
            int num = calories[right++];
            windowSum += num;

            while (right - left == k) {
                if (windowSum > upper) {
                    ++totalPoints;
                } else if (windowSum < lower) {
                    --totalPoints;
                }
                int num = calories[left++];
                windowSum -= num;
            }
        }

        return totalPoints;
    }
};