[HDOJ1811]Rank of Tetris(并查集、拓扑排序)

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=1811

求一堆数据的拓扑序。

处理：x>y就是x到y一条边，x<y就是y到x一条边。关键问题是处理x=y的情况。

假如x=y，就有问题了。假如不处理的话，可能会被当成少处理一个点而使结果编程UNCERTAIN。所以我们考虑用并查集来解决这个问题。

选谁当祖先？题中又给了一个其他的量叫做RP值，这个RP值的规律是序号越大RP值越大。这样我们可以在合并的时候，尽可能地将RP值大的数当成本集合的祖先。

 /*
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 ┓┏┓┏┓┃キリキリ♂ mind！
 ┛┗┛┗┛┃＼○／
 ┓┏┓┏┓┃ /
 ┛┗┛┗┛┃ノ)
 ┓┏┓┏┓┃
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 ┃┃┃┃┃┃
 ┻┻┻┻┻┻
 */
 #include <algorithm>
 #include <iostream>
 #include <iomanip>
 #include <cstring>
 #include <climits>
 #include <complex>
 #include <fstream>
 #include <cassert>
 #include <cstdio>
 #include <bitset>
 #include <vector>
 #include <deque>
 #include <queue>
 #include <stack>
 #include <ctime>
 #include <set>
 #include <map>
 #include <cmath>
 using namespace std;
 #define fr first
 #define sc second
 #define cl clear
 #define BUG puts("here!!!")
 #define W(a) while(a--)
 #define pb(a) push_back(a)
 #define Rint(a) scanf("%d", &a)
 #define Rll(a) scanf("%lld", &a)
 #define Rs(a) scanf("%s", a)
 #define Cin(a) cin >> a
 #define FRead() freopen("in", "r", stdin)
 #define FWrite() freopen("out", "w", stdout)
 #define Rep(i, len) for(int i = 0; i < (len); i++)
 #define For(i, a, len) for(int i = (a); i < (len); i++)
 #define Cls(a) memset((a), 0, sizeof(a))
 #define Clr(a, x) memset((a), (x), sizeof(a))
 #define Full(a) memset((a), 0x7f7f, sizeof(a))
 #define lp p << 1
 #define rp p << 1 | 1
 #define pi 3.14159265359
 #define RT return
 #define lowbit(x) x & (-x)
 #define onenum(x) __builtin_popcount(x)
 typedef long long LL;
 typedef long double LD;
 typedef unsigned long long ULL;
 typedef pair<int, int> pii;
 typedef pair<string, int> psi;
 typedef map<string, int> msi;
 typedef vector<int> vi;
 typedef vector<LL> vl;
 typedef vector<vl> vvl;
 typedef vector<bool> vb;

 typedef struct Edge {
     int u, v, next;
     Edge() {}
     Edge(int uu, int vv) : u(uu), v(vv) { next = -; }
 }Edge;
 const int maxn = ;
 const int maxm = ;
 int n, m;
 Edge edge[maxm];
 int head[maxn];
 int hcnt;
 int pre[maxn];
 int in[maxn];
 int num, q[maxn], front, tail;
 int uu[maxn], vv[maxn];
 char cc[maxn][];

 void adde(int u, int v) {
     edge[hcnt] = Edge(u, v);
     edge[hcnt].next = head[u];
     head[u] = hcnt++;
     in[v]++;
 }

 int find(int x) {
     RT x == pre[x] ? x : pre[x] = find(pre[x]);
 }

 int unite(int x, int y) {
     int fx = find(x);
     int fy = find(y);
     if(fx == fy) RT ;
     if(x > y) pre[fy] = fx;
     else pre[fx] = fy;
     return ;

 }

 int topo() {
     front = tail = ;
     Rep(i, n) {
         if(in[i] ==  && i == find(i)) {
             q[tail++] = i;
         }
     }
     int ret = ;
     while(front < tail) {
         if(tail - front > ) ret = ;
         int u = q[front++];
         --num;
         for(int i = head[u]; ~i; i=edge[i].next) {
             int v = edge[i].v;
             if(--in[v] == ) {
                 q[tail++] = v;
             }
         }
     }
     if(num > ) printf("CONFLICT\n");
     else if(ret) printf("UNCERTAIN\n");
     else printf("OK\n");
 }

 int main() {
     // FRead();
     int u, v;
     while(~Rint(n) && ~Rint(m)) {
         Cls(in); Clr(head, -); hcnt = ;
         num = n;
         Rep(i, n+) pre[i] = i;
         Rep(i, m) {
             Rint(uu[i]); Rs(cc[i]); Rint(vv[i]);
             if(cc[i][] == '=') {
                 if(unite(uu[i], vv[i])) num--;
             }
         }
         Rep(i, m) {
             if(cc[i][] != '=') {
                 u = find(uu[i]); v = find(vv[i]);
                 if(cc[i][] == '>') adde(u, v);
                 if(cc[i][] == '<') adde(v, u);
             }
         }
         topo();
     }
     RT ;
 }