LA 4255 (拓扑排序 并查集) Guess

设这个序列的前缀和为S_i(0 <= i <= n)，S₀ = 0

每一个符号对应两个前缀和的大小关系，然后根据这个关系拓扑排序一下。

还要注意一下前缀和相等的情况，所以用一个并查集来查询。

 1 #include <cstdio>
 2 #include <cstring>
 3
 4 const int maxn = 15;
 5 int n;
 6 int G[maxn][maxn];
 7 char s[100];
 8 int sum[maxn], a[maxn];
 9
10 int topo[maxn], c[maxn], t;
11
12 void dfs(int u)
13 {
14     c[u] = 1;
15     for(int v = 0; v <= n; v++) if(G[u][v] && !c[v]) dfs(v);
16     topo[--t] = u;
17 }
18
19 void toposort()
20 {
21     t = n + 1;
22     memset(c, 0, sizeof(c));
23     for(int u = 0; u <= n; u++) if(!c[u]) dfs(u);
24 }
25
26 int p[maxn];
27 int find(int x)
28 { return x == p[x] ? x : p[x] = find(p[x]); }
29
30 void link(int x, int y)
31 {
32     int px = find(x), py = find(y);
33     if(px != py) p[px] = py;
34 }
35
36 int main()
37 {
38     //freopen("in.txt", "r", stdin);
39
40     int T; scanf("%d", &T);
41     while(T--)
42     {
43         scanf("%d", &n);
44         scanf("%s", s);
45
46         for(int i = 0; i <= n; i++) p[i] = i;
47
48         memset(G, 0, sizeof(G));
49         int p = 0;
50         for(int i = 1; i <= n; i++)
51             for(int j = i; j <= n; j++)
52             {
53                 if(s[p] == ‘+‘) G[i-1][j]++;
54                 if(s[p] == ‘-‘) G[j][i-1]++;
55                 if(s[p] == ‘0‘) link(i-1, j);
56                 p++;
57             }
58         toposort();
59         for(p = 0; p <= n; p++) if(topo[p] == 0) break;
60         s[0] = 0;
61
62         for(int i = p + 1; i <= n; i++)
63         {
64             int s1 = topo[i], s2 = topo[i-1];
65             if(find(s1) == find(s2)) sum[s1] = sum[s2]; //前缀和相等
66             else sum[s1] = sum[s2] + 1;
67         }
68         for(int i = p - 1; i >= 0; i--)
69         {
70             int s1 = topo[i], s2 = topo[i+1];
71             if(find(s1) == find(s2)) sum[s1] = sum[s2];
72             else sum[s1] = sum[s2] - 1;
73         }
74         for(int i = 1; i <= n; i++)
75         {
76             if(i > 1) printf(" ");
77             printf("%d", sum[i] - sum[i - 1]);
78         }
79         puts("");
80     }
81
82     return 0;
83 }

代码君