in the nested loop when i=j=0 at that point currentSum =cumSum[j]-cumSum[i-1] is going to be garbage value as i=0. therefor i-1 becomes -1. which is not possible
in the nested loop when i=j=0 at that point currentSum =cumSum[j]-cumSum[i-1] is going to be garbage value as i=0. therefor i-1 becomes -1. which is not possible