Algorithm: POJ 3905 Perfect election (2-sat simple to judge)

Ideas

2-sat a simple judgment question

Code

#include <iostream> #include <queue> #include <cstdio> #include <cstring> using namespace std  
    
;  
const int MAXN = 1010;  
const int VN = MAXN*2;  
    
const int EN = VN*VN*2;  
    
     
int n, m;  
struct edge{int V, next;  
    
};  
    struct graph{int size, HEAD[VN];  
    Edge E[en];  
    void Init () {size=0; memset (Head,-1, sizeof (head));  
        void Addedge (int u, int v) {e[size].v = v;  
        E[size].next = Head[u];  
    Head[u] = size++;  
    
}}g;  
        Class two_sat{Public:bool Check (const graph& g, const int n) {SCC (g, 2*n);  
        for (int i=0; i<n; ++i) if (belong[i] = = Belong[i+n]) return false;  
    return true;   
        } private:void Tarjan (const graph& g, const int u) {int V;  
        Low[u] = dfn[u] = ++idx;  
        sta[top++] = u;  
    
        Instack[u] = true; for (int e=g.head[u]; E!=-1 E=g.e[e].next) {v = g.e[e].v;  
                if (dfn[v] = =-1) {Tarjan (g, v);  
            Low[u] = min (Low[u], low[v]);  
            }else if (Instack[v]) {Low[u] = min (Low[u], dfn[v]);  
            } if (dfn[u] = = Low[u]) {++bcnt;  
                do{v = sta[--top];  
                INSTACK[V] = false;  
            BELONG[V] = bcnt;  
        }while (U!= v);  
        } void SCC (const graph& g, const int n) {bcnt = idx = top = 0;  
        memset (DFN,-1, sizeof (DFN));  
        memset (instack, 0, sizeof (instack));  
    for (int i=0; i<n; ++i) if (dfn[i] = = 1) Tarjan (g, I);  
    } private:int idx, top, bcnt;  
    int DFN[VN], low[vn], BELONG[VN], STA[VN];  
BOOL INSTACK[VN];  
    
}sat;  
    int main () {int A, B;  
    
       while (~SCANF ("%d%d", &n, &m)) { G.init ();  
    
            for (int i=0; i<m; ++i) {scanf ("%d%d", &a, &b);  
                if (a>0 && b>0) {//+ +--a;--b;  
                G.addedge (a+n, b);  
    
            G.addedge (B+n, a);    
                }else if (a>0 && b<0) {//+-B =-C; --a;  
                --b;  
                G.addedge (A+n, b+n);  
    
            G.addedge (b, a);  
                }else if (a<0 && b>0) {//-+ a =-A; --a;  
                --b;   
                G.addedge (A, b);  
    
            G.addedge (B+n, a+n);  
                }else if (a<0 && b<0) {//--A =-A; b =-A; --a;  
                --b;  
                G.addedge (A, b+n);  
            G.addedge (b, a+n);  
        } if (Sat.check (g, N)) puts ("1");  
        
    Else puts ("0");  
return 0; }

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