feat(#1176): solve the problem #1176.Diet Plan Performance

Author: geemo

1176.Diet Plan Performance/README.md

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+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.
+```
+
+**Constraints:**
+
+- 1 <= k <= calories.length <= 10^5
+- 0 <= calories[i] <= 20000
+- 0 <= lower <= upper
+
+**Solution:**
+
+```golang
+func dietPlanPerformance(calories []int, k int, lower int, upper int) int {
+  left, sum, score, cLen := 0, 0, 0, len(calories)
+  for right := 0; right < cLen; right++ {
+    sum += calories[right]
+    if (right - left + 1) == k {
+      if sum > upper {
+        score++
+      } else if sum < lower {
+        score--
+      }
+      sum -= calories[left]
+      left++
+    }
+  }
+
+  return score
+}
+```