The meaning of problems: there are n boys, m girls, boys selected from no less than four boys, girls selected less than a girl, t make up for the number of teams asked several possible combinations?
Thinking: permutations problem, the number of combinations and Triangle one correspondence, according to Pascal's triangle results
Code:
#include <iostream> using namespace std; typedef long long LL; The Y LL [ 70 ] [ 70 ]; // configured Pascal's triangle void the init () { for ( int I = 0 ; I <= 30 ; I ++ ) { Y[i][0]=1; for(int j = 1; j <= i; j++) { Y[i][j] = Y[i-1][j-1] + Y[i-1][j]; } } } int main () { init(); int n, m, t; cin >> n >> m >> t; LL res = 0; for(int i = 4; i < t; i++) { res += Y[n][i] * Y[m][t-i]; } cout << res << endl; return 0; }