[2016-03-07][UVALive][3212][Crime]

时间:2016-03-06 13:51:13 星期日
题目编号:[UVALive][3212][Crime]
题目大意:端点交替着色黑白,求黑色的最少着色数
输入:

若干组数据
每组数据

n m 顶点数,边数
接下去m行,边

输出:黑色最少着色数,如果不能黑白间隔那么就输出Impossible
分析:

题目有若干个联通块,最后答案就是每个联通块最少着色数目之和,

直接dfs对每个点交替着色,如果遇到已经着色的并且颜色一样,那么一定不能完成着色
通过对两种着色的情况进行计数,最后得到最小着色数目,(而重新设置初始条件再跑一遍dfs比较两次的值)
方法:dfs每个端点,每到一个端点没着色就着色,直到无法着色,如果遇到边两端颜色一样,就Impossible

#include <vector>

#include <list>

#include <map>

#include <set>

#include <deque>

#include <queue>

#include <stack>

#include <bitset>

#include <algorithm>

#include <functional>

#include <numeric>

#include <utility>

#include <sstream>

#include <iostream>

#include <iomanip>

#include <cstdio>

#include <cmath>

#include <cstdlib>

#include <cctype>

#include <string>

#include <cstring>

#include <cstdio>

#include <cmath>

#include <cstdlib>

#include <ctime>

using namespace std;

typedef long long LL;

#define CLR(x,y) memset((x),(y),sizeof((x)))

#define FOR(x,y,z) for(int (x)=(y);(x)<(z);++(x))

#define FORD(x,y,z) for(int (x)=(y);(x)>=(z);--(x))

#define FOR2(x,y,z) for((x)=(y);(x)<(z);++(x))

#define FORD2(x,y,z) for((x)=(y);(x)>=(z);--(x))

int n,m;

const int maxn = 1000 + 10;

const int maxedge = maxn*maxn;

int head[maxn];

int nextt[maxedge];

int endd[maxedge];

void addedge(int from,int to){

static int q = 2;

endd[q] = to;

nextt[q] = head[from];

head[from] = q++;

}

void ini(){

memset(head,-1,sizeof(head));

}

int vis[maxn],cnt[2];

int dfs(int u){

++cnt[vis[u]];

for(int q = head[u];~q;q = nextt[q]){

int v = endd[q];

if(vis[v] == -1){

vis[v] = 1 - vis[u];

if(dfs(v)) return 1;

}

if(vis[u] == vis[v]) return 1;

}

return 0;

}

int main(){

//freopen("in.txt","r",stdin);

//freopen("out.txt","w",stdout);

while(~scanf("%d%d",&n,&m)){

int u1,v1,fnlres = 0;ini();

FOR(i,0,m){

scanf("%d%d",&u1,&v1);

addedge(u1,v1);

addedge(v1,u1);

}

CLR(vis,-1);

FOR(i,1,n+1){

if(vis[i] == -1 && ~head[i]){

cnt[0] = cnt[1] = vis[i] = 0;

if(!dfs(i)) fnlres += min(cnt[0],cnt[1]);

else{

fnlres = -1;

break;

}

if(~fnlres) printf("%d\n",fnlres);

else puts("Impossible");

}

return 0;

}

来自为知笔记(Wiz)

来源：https://www.cnblogs.com/qhy285571052/p/5251806.html

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