Find subarray in integer array with least average in single loop

Question

Given an integer array and size of subarray, find the first subarray with leat average in single loop. Print first index of subarray and average. Problem is I can't use variable substring length c without using any additional loop. My code is-

public void FindFirstSub(int a[], int b, int c)
{
    int average=0,sum=0,leastav=0;
    for(int i=0;i<a.length-c;i++)
    {
        sum = 0;
        sum = a[i]+a[i+1]+a[i+2]; // Here is problem.
        System.out.print(a[i]+" "+a[i+1]+" "+a[i+2]+"\n");
        average = sum/c;
        if(leastav==0)
            leastav=average;
        else if(leastav>average)
            leastav=average;
    }
    System.out.println("Least average is "+leastav);
}

I cannot understand what you want to do. In the line with //Here is problem comment, it will fail when the i becomes length-1. Also as @MohinuddinLuhar said, it will fail for c > a.length. What is the usage of int b?. Are you sure that you know what you try to do? — Ioannis Barakos, Oct 07 '19 at 14:15

score 0 · Answer 1 · answered Oct 07 '19 at 16:01

You need to set sum to 0 outside of your for loop and keep a running total for sum. With every iteration, subtract the first element of the previous sub-array while adding the new last element of the new sub-array. You shouldn't start subtracting till you reach your second sub-array or checking for averages until 'i' is the last index of the first sub-array.

score 0 · Answer 2 · answered Oct 08 '19 at 05:43

You can't use the single loop only to find the least average but complexity you can maintain till O(n).

        static void FindFirstSub(int arr[],int n, int k) 
            { 
              if (n < k) 
                 return; 

            int res_index = 0; 

            int curr_sum = 0; 
            for (int i = 0; i < k; i++) 
                curr_sum += arr[i]; 

            // Initialize minimum sum as current sum 
            int min_sum = curr_sum; 

            for (int i = k; i < n; i++)  
            { 
                // Add current item and remove first 
                // item of previous subarray 
                curr_sum += arr[i] - arr[i - k]; 

                // Update result if needed 
                if (curr_sum < min_sum) { 
                    min_sum = curr_sum; 
                    res_index = (i - k + 1); 
                } 
            } 

            System.out.println("Subarray btw [" + 
                                res_index + ", " + (res_index + k - 1) + 
                                "] has minimum average"); 
        } 

        // Driver method to test the above function 
        public static void main(String[] args) 
        {   
            int arr[] = { 3, 7, 90, 20, 10, 50, 40 }; 
            int k = 3; // Subarray size 
           FindFirstSub(arr.length, k); 
        }

Find subarray in integer array with least average in single loop

2 Answers2