hdu 1811 Rank of Tetris (并查集+拓扑排序)

　　感觉这题的并查集以及拓扑排序并不难，但是做题的时候必须理解到矛盾(CONFLICT)与不确定(UNCERTAIN)直接的优先关系。

　　做这题的时候，构图什么的很简单，就是没有将矛盾摆在最高优先，一旦搜到不确定的情况就立即跳转，这是不对的。

代码如下：

  1 #include <set>
  2 #include <cstdio>
  3 #include <cstring>
  4 #include <iostream>
  5 #include <algorithm>
  6 
  7 using namespace std;
  8 
  9 const int N = 11111;
 10 struct MFS {
 11     int fa[N];
 12     void init() { for (int i = 0; i < N; i++) fa[i] = i;}
 13     int find(int x) { return fa[x] = fa[x] == x ? x : find(fa[x]);}
 14     void merge(int x, int y) {
 15         int fx = find(x), fy = find(y);
 16         if (fx == fy) return ;
 17         fa[fx] = fy;
 18     }
 19 } mfs;
 20 
 21 int x[N << 1], y[N << 1], inarc[N];
 22 bool used[N];
 23 char op[N << 1][3];
 24 
 25 struct Edge {
 26     int t, nx;
 27     Edge() {}
 28     Edge(int t, int nx) : t(t), nx(nx) {}
 29 } edge[N << 1];
 30 int eh[N], ec;
 31 
 32 void init() {
 33     mfs.init();
 34     memset(used, 0, sizeof(used));
 35     memset(inarc, 0, sizeof(inarc));
 36     memset(eh, -1, sizeof(eh));
 37     ec = 0;
 38 }
 39 
 40 void addedge(int s, int t) {
 41     edge[ec] = Edge(t, eh[s]);
 42     eh[s] = ec++;
 43 }
 44 
 45 typedef pair<int, int> PII;
 46 set<PII> nodes;
 47 
 48 void input(int n, int m) {
 49     init();
 50     for (int i = 0; i < m; i++) {
 51         scanf("%d%s%d", &x[i], op[i], &y[i]);
 52         if (op[i][0] == '=') mfs.merge(x[i], y[i]);
 53         else if (op[i][0] == '<') inarc[x[i]]++;
 54         else if (op[i][0] == '>') inarc[y[i]]++;
 55     }
 56     for (int i = 0; i < n; i++) {
 57         int rt = mfs.find(i);
 58         used[rt] = true;
 59         if (rt != i) inarc[rt] += inarc[i];
 60     }
 61 //    for (int i = 0; i < n; i++) {
 62 //        if (!vis[i]) continue;
 63 //        cout << i << '~' << inarc[i] << ": ";
 64 //        for (int t = eh[i]; ~t; t = edge[t].nx) cout << edge[t].t << ' ';
 65 //        cout << endl;
 66 //    }
 67 }
 68 
 69 int topo(int n, int m) {
 70     for (int i = 0; i < m; i++) {
 71         if (op[i][0] == '<') {
 72             if (mfs.fa[x[i]] == mfs.fa[y[i]]) return -2;
 73             addedge(mfs.fa[y[i]], mfs.fa[x[i]]);
 74         }
 75         if (op[i][0] == '>') {
 76             if (mfs.fa[x[i]] == mfs.fa[y[i]]) return -2;
 77             addedge(mfs.fa[x[i]], mfs.fa[y[i]]);
 78         }
 79     }
 80     nodes.clear();
 81     for (int i = 0; i < n; i++) if (used[i]) nodes.insert(PII(inarc[i], i));
 82     PII tmp;
 83     bool unc = false;
 84     while (!nodes.empty()) {
 85         tmp = *nodes.begin();
 86 //        cout << tmp.first << ' ' << tmp.second << endl;
 87         nodes.erase(nodes.begin());
 88         if (tmp.first) return -2;
 89         if (!nodes.empty() && (*nodes.begin()).first == 0) unc = true;
 90         for (int t = eh[tmp.second]; ~t; t = edge[t].nx) {
 91             int id = edge[t].t;
 92             if (inarc[id] < 0) {
 93                 cout << "shit!" << endl;
 94                 while (1) ;
 95             }
 96             nodes.erase(PII(inarc[id], id));
 97             nodes.insert(PII(--inarc[id], id));
 98         }
 99     }
100     return unc;
101 }
102 
103 int main() {
104 //    freopen("in", "r" ,stdin);
105     int n, m;
106     while (~scanf("%d%d", &n, &m)) {
107         input(n, m);
108         int ans = topo(n, m);
109 //        cout << ans << endl;
110         if (ans == 0) puts("OK");
111         else if (ans == 1) puts("UNCERTAIN");
112         else puts("CONFLICT");
113     }
114     return 0;
115 }

View Code

——written by Lyon

posted @ 2013-07-23 02:24 LyonLys 阅读(220) 评论(0) 编辑收藏举报

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