Can somebody give me the whole explanation to this problem. Thanks beforehand!

If you have two different sets A = {a1, a2, a3} and B = {b1, b2, b3, b4} then we have |A| * |B| = 3 * 4 = 12 ways to choose a pair (a[i], b[j]).

i\j   b[1]  b[2]  b[3]  b[4]
a[1] [1,1] [1,2] [1,3] [1,4]
a[2] [2,1] [2,2] [2,3] [2,4]
a[3] [3,1] [3,2] [3,3] [3,4]

Modern language solution looks like that:
map<string, int> cnt;
for (auto color : {"Blue", "Red", "Yellow"})
  cin >> cnt[color];

int colors;
cin >> colors;

int ways = 1;
for (int i = 0; i < colors; i++)
{
  string color;
  cin >> color;

  ways *= cnt[color];
}

cout << ways;

Edited by author 24.11.2016 16:04

Edited by author 24.11.2016 16:07