UVALive

题目链接：https://cn.vjudge.net/problem/UVALive-3211

【AC代码】

#include<cstdlib>#include<cstdio>#include<cstring>#include<cmath>#include<algorithm>#include<vector>#include<map>#include<stack>#include<set>using namespace std;#define LL long longconst int maxn = 50000 + 5;struct TwoSAT{    int n;    vector<int>G[maxn*2];    bool mark[maxn*2];    int s[maxn*2], c;    bool dfs(int x)    {        if(mark[x^1])return false;        if(mark[x])return true;        mark[x] = true;        s[c++] = x;        for(int i = 0; i < G[x].size(); i++)        {            if(!dfs(G[x][i]))return false;        }        return true;    }    void init(int n)    {        this->n = n;        for(int i = 0; i < n*2; i++)        {            G[i].clear();        }        memset(mark, 0, sizeof(mark));    }    void add_caluse(int x, int xval, int y, int yval)    {        x = x*2 + xval;        y = y*2 + yval;        G[x^1].push_back(y);        G[y^1].push_back(x);    }    bool solve()    {        for(int i = 0; i < n*2; i+=2)        {            if(!mark[i]&&!mark[i+1])            {                c = 0;                if(!dfs(i))                {                    while(c > 0)                    {                        mark[s[--c]] = false;                    }                    if(!dfs(i+1))                    {                        return false;                    }                }            }        }        return true;    }};TwoSAT solver;int n,T[maxn][2];bool test(int diff){    solver.init(n);    for(int i = 0; i < n; i++)    {        for(int a = 0; a < 2; a++)        {            for(int j = i+1; j < n; j++)            {                for(int b = 0; b < 2; b++)                {                    if(abs(T[i][a]-T[j][b]) < diff)                    {                        solver.add_caluse(i, a^1, j, b^1);                    }                }            }        }    }    return solver.solve();}int main(){    while(~scanf("%d", &n))    {        if(n == 0)break;        int L = 0, R = 0;        for(int i = 0; i < n; i++)for(int a = 0; a < 2; a++)        {            scanf("%d",&T[i][a]);            R = max(R, T[i][a]);        }        while(L < R)        {            int M = L + (R - L + 1)/2;            if(test(M))L = M;            else R = M - 1;        }        printf("%d\n",L);    }    return 0;}