[Codility] Prefix Sums - MinAvgTwoSlice / Java

1. 문제

A non-empty array A consisting of N integers is given. A pair of integers (P, Q), such that 0 ≤ P < Q < N, is called a slice of array A (notice that the slice contains at least two elements). The average of a slice (P, Q) is the sum of A[P] + A[P + 1] + ... + A[Q] divided by the length of the slice. To be precise, the average equals (A[P] + A[P + 1] + ... + A[Q]) / (Q − P + 1).

For example, array A such that:

A[0] = 4 A[1] = 2 A[2] = 2 A[3] = 5 A[4] = 1 A[5] = 5 A[6] = 8

contains the following example slices:

• slice (1, 2), whose average is (2 + 2) / 2 = 2;
• slice (3, 4), whose average is (5 + 1) / 2 = 3;
• slice (1, 4), whose average is (2 + 2 + 5 + 1) / 4 = 2.5.

The goal is to find the starting position of a slice whose average is minimal.

Write a function:

class Solution { public int solution(int[] A); }

that, given a non-empty array A consisting of N integers, returns the starting position of the slice with the minimal average. If there is more than one slice with a minimal average, you should return the smallest starting position of such a slice.

For example, given array A such that:

A[0] = 4 A[1] = 2 A[2] = 2 A[3] = 5 A[4] = 1 A[5] = 5 A[6] = 8

the function should return 1, as explained above.

Write an efficient algorithm for the following assumptions:

• N is an integer within the range [2..100,000];
• each element of array A is an integer within the range [−10,000..10,000].

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2. 코드

class Solution {
    public int solution(int[] A) {
        
        int minIndex = 0;
        float min = Float.MAX_VALUE;
        
        for(int i=0; i<A.length-1; i++) {
            int sum = A[i];
            int count = 1;
            for(int j=i+1; j<A.length; j++) {
                sum += A[j];
                count++;
                float avg = (float)sum / (float)count;
                
                if(avg < min) {
                    min = avg;
                    minIndex = i;
                }
                
                if(count==3)
                    break;
                    
            }
        }
        
        return minIndex;
    }
}