HDU-1331 Function Run Fun （记忆化搜索）

#include<bits/stdc++.h>
using namespace std;
int w[21][21][21];

int dfs(int a, int b, int c) {
if (a <= 0 || b <= 0 || c <= 0) return 1;
if (~w[a][b][c]) return w[a][b][c];
if (a < b && b < c) return w[a][b][c] = dfs(a, b, c-1) + dfs(a, b-1, c-1) - dfs(a, b-1, c);
else return w[a][b][c] = dfs(a-1, b, c) + dfs(a-1, b-1, c) + dfs(a-1, b, c-1) - dfs(a-1, b-1, c-1);
}

int main() {
int a, b, c, ans;
memset(w, -1, sizeof(w));
while(~scanf("%d%d%d", &a, &b, &c)) {
if (a == -1 && b == -1 && c == -1) break;
if (a <= 0 || b <= 0 || c <= 0) ans = 1;
else if (a > 20 || b > 20 || c > 20) ans = dfs(20, 20, 20);
else ans = dfs(a, b, c);
printf("w(%d, %d, %d) = %d\n", a, b, c, ans);
}

return 0;
}