Question

link

Given an array of integers and a number x, find the smallest subarray with sum greater than the given value.

Eg. input = (1, 4, 45, 6, 0, 19), 51, output (4, 45, 6)

Solution

Solution 1 (the better one) is based on another question Subarray with 0 Sum. We calculate the 前缀和 of every number. Takes O(n) time.

If all input are positive, there can be a Solution 2 which is based on another question Subarray with Particular Sum. The sliding window search. It’s O(n) time as well.

Code

Solution 2 (for positive input) 

int smallestSubWithSum(int arr[], int n, int x) {
    //  Initilize length of smallest subarray as n+1
     int min_len = n + 1;

     // Pick every element as starting point
     for (int start=0; start<n; start++)
     {
          // Initialize sum starting with current start
          int curr_sum = arr[start];

          // If first element itself is greater
          if (curr_sum > x) return 1;

          // Try different ending points for curremt start
          for (int end=start+1; end<n; end++)
          {
              // add last element to current sum
              curr_sum += arr[end];

              // If sum becomes more than x and length of
              // this subarray is smaller than current smallest
              // length, update the smallest length (or result)
              if (curr_sum > x && (end - start + 1) < min_len)
                 min_len = (end - start + 1);
          }
     }
     return min_len;
}