Find a big-O estimate for the running time (in terms of n) of the following function (with explanation):

(a) int mysterySum( int n ) {

int i, j, s=0;

for(i=0; i < n; i++) {

for(j=0; j < i; j++) {

s += i*i;

}

}

}

(b) Replace the inner loop in mysterySum by an O(1) expression and compute the running time of the new program.