hdu 2647 Reward

Dandelion's uncle is a boss of a factory. As the spring festival is coming , he wants to distribute rewards to his workers. Now he has a trouble about how to distribute the rewards. 
The workers will compare their rewards ,and some one may have demands of the distributing of rewards ,just like a's reward should more than b's.Dandelion's unclue wants to fulfill all the demands, of course ,he wants to use the least money.Every work's reward will be at least 888 , because it's a lucky number.

Input

One line with two integers n and m ,stands for the number of works and the number of demands .(n<=10000,m<=20000) 
then m lines ,each line contains two integers a and b ,stands for a's reward should be more than b's.

Output

For every case ,print the least money dandelion 's uncle needs to distribute .If it's impossible to fulfill all the works' demands ,print -1.

Sample Input

2 1
1 2
2 2
1 2
2 1

Sample Output

1777
-1

---

　　反向建图，跑拓扑排序即可。

Code

/**
 * hdu
 * Problem#2647
 * Accepted
 * Time:31ms
 * Memory:1976k
 */
#include <iostream>
#include <cstdio>
#include <ctime>
#include <cmath>
#include <cctype>
#include <cstring>
#include <cstdlib>
#include <fstream>
#include <sstream>
#include <algorithm>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <vector>
#include <stack>
#ifndef WIN32
#define Auto "%lld"
#else
#define Auto "%I64d"
#endif
using namespace std;
typedef bool boolean;
const signed int inf = (signed)((1u << 31) - 1);
const double eps = 1e-6;
const int binary_limit = 128;
#define smin(a, b) a = min(a, b)
#define smax(a, b) a = max(a, b)
#define max3(a, b, c) max(a, max(b, c))
#define min3(a, b, c) min(a, min(b, c))
template<typename T>
inline boolean readInteger(T& u){
    char x;
    int aFlag = 1;
    while(!isdigit((x = getchar())) && x != '-' && x != -1);
    if(x == -1) {
        ungetc(x, stdin);    
        return false;
    }
    if(x == '-'){
        x = getchar();
        aFlag = -1;
    }
    for(u = x - '0'; isdigit((x = getchar())); u = (u << 1) + (u << 3) + x - '0');
    ungetc(x, stdin);
    u *= aFlag;
    return true;
}

///map template starts
typedef class Edge{
    public:
        int end;
        int next;
        Edge(const int end = 0, const int next = 0):end(end), next(next){}
}Edge;

typedef class MapManager{
    public:
        int ce;
        int *h;
        Edge *edge;
        MapManager(){}
        MapManager(int points, int limit):ce(0){
            h = new int[(const int)(points + 1)];
            edge = new Edge[(const int)(limit + 1)];
            memset(h, 0, sizeof(int) * (points + 1));
        }
        inline void addEdge(int from, int end){
            edge[++ce] = Edge(end, h[from]);
            h[from] = ce;
        }
        inline void addDoubleEdge(int from, int end){
            addEdge(from, end);
            addEdge(end, from);
        }
        Edge& operator [] (int pos) {
            return edge[pos];
        }
        inline void clear() {
            delete[] edge;
            delete[] h;
        }
}MapManager;
#define m_begin(g, i) (g).h[(i)]
///map template ends

int n, m;
MapManager g;
int* dag;
int* dep;

inline boolean init() {
    if(!readInteger(n))    return false;
    readInteger(m);
    g = MapManager(n, m);
    dag = new int[(n + 1)];
    dep = new int[(n + 1)];
    memset(dag, 0, sizeof(int) * (n + 1));
    memset(dep, -1, sizeof(int) * (n + 1));
    for(int i = 1, a, b; i <= m; i++) {
        readInteger(a);
        readInteger(b);
        g.addEdge(b, a);
        dag[a]++;
    }
    return true;
}

queue<int> que;
inline void topu() {
    for(int i = 1; i <= n; i++)
        if(!dag[i])
            dep[i] = 888, que.push(i);
    while(!que.empty()) {
        int e = que.front();
        que.pop();
        for(int i = m_begin(g, e); i; i = g[i].next) {
            int& eu = g[i].end;
            dag[eu]--;
            smax(dep[eu], dep[e] + 1);
            if(!dag[eu])
                que.push(eu);
        }
    }
}

int res;
inline void solve() {
    res = 0;
    topu();
    for(int i = 1; i <= n; i++) {
        if(dag[i]) {
            puts("-1");
            return;
        }
        res += dep[i];
    }
    printf("%d
", res);
}

inline void clear() {
    g.clear();
    delete[] dep;
    delete[] dag;
}

int main() {
    while(init()) {
        solve();
        clear();
    }
    return 0;
}