P3154 [CQOI2009]循环赛

https://www.luogu.com.cn/record/85829701

Luogu/P3154/P3154.cpp

@@ -0,0 +1,108 @@
+#include <cstdio>
+#include <cctype>
+
+const int N = 10;
+
+int n, a[N], s[N], ans;
+
+template <typename T>
+void read(T& x) {
+    x = 0;
+    char c = getchar();
+    int f = 1;
+
+    while (!isdigit(c)) {
+        if (c == '-') f = -1;
+        c = getchar();
+    }
+
+    while (isdigit(c)) {
+        x = x * 10 + (c - '0');
+        c = getchar();
+    }
+
+    x *= f;
+}
+
+void dfs(int x, int y) {
+    // 当前得分已经大于最终得分
+    if (s[x] > a[x]) return;
+
+    // 如果以后的比赛全赢也小于最后的分数
+    if (s[x] + (n - y + 1) * 3 < a[x]) return;
+
+    if (x == n && s[x] == a[x]) {
+        ans++;
+        return;
+    }
+
+    if (y == n) {
+        int t = a[x] - s[x];
+
+        // 最后一场比赛无法凑出 2 分
+        switch (t) {
+            case 0: {
+                s[y] += 3;
+                dfs(x + 1, x + 2);
+                s[y] -= 3;
+
+                break;
+            }
+
+            case 1: {
+                s[x] += 1;
+                s[y] += 1;
+                dfs(x + 1, x + 2);
+                s[x] -= 1;
+                s[y] -= 1;
+
+                break;
+            }
+
+            case 3: {
+                s[x] += 3;
+                dfs(x + 1, x + 2);
+                s[x] -= 3;
+
+                break;
+            }
+        }
+
+        return;
+    }
+
+    // x 胜
+    s[x] += 3;
+    s[y] += 0;
+    dfs(x, y + 1);
+    s[x] -= 3;
+    s[y] -= 0;
+
+    // 平局
+    s[x] += 1;
+    s[y] += 1;
+    dfs(x, y + 1);
+    s[x] -= 1;
+    s[y] -= 1;
+
+    // y 胜
+    s[x] += 0;
+    s[y] += 3;
+    dfs(x, y + 1);
+    s[x] -= 0;
+    s[y] -= 3;
+}
+
+int main() {
+    read(n);
+
+    for (int i = 1; i <= n; i++) {
+        read(a[i]);
+    }
+
+    dfs(1, 2);
+
+    printf("%d\n", ans);
+
+    return 0;
+}