Codeforces Round #376 (Div. 2) C dfs+并查集

来源：互联网发布：必应词典网络连接超时编辑：程序博客网时间：2024/05/10 16:09

题目传送门： http://codeforces.com/contest/731/problem/C

题意：有k有颜色，n天，m只袜子（n,m,k<=200000），每只袜子都有一个颜色，每天穿两只袜子a,b，问最少要改变多少只袜子的颜色才能使他每天都穿同种颜色的袜子

思路：先用邻接表建图，然后dfs找联通图，记录联通图中节点个数s和联通图中使用颜色最多的哪个颜色的个数c，然后s-c就是该联通图中需要改变的颜色数，最后把所有联通图的加起来就是答案

需要注意的是，当记录颜色时，数组用完要再dfs一遍清除或memset m长度的该数组，不要直接全部mem，会T

代码如下：

#include <iostream>#include <algorithm>#include <cstring>#include <stdio.h>#include <string>#include <cmath>#include <queue>#include <set>#include <map>#include <vector>using namespace std;#define   lson          l,m,rt<<1#define   rson          m+1,r,rt<<1|1#define   ll            long long#define   ull           unsigned long long#define   mem(n,v)      memset(n,v,sizeof(n))#define   MAX           200005#define   MAXN          1000005#define   PI            3.1415926#define   E             2.718281828459#define   opnin         freopen("text.in.txt","r",stdin)#define   opnout        freopen("text.out.txt","w",stdout)#define   clsin         fclose(stdin)#define   clsout        fclose(stdout)#define   haha1         cout << "haha1"<< endl#define   haha2         cout << "haha2"<< endl#define   haha3         cout << "haha3"<< endlconst int    INF    =   0x3f3f3f3f;const ll     INFF   =   0x3f3f3f3f3f3f3f3f;const double pi     =   3.141592653589793;const double inf    =   1e18;const double eps    =   1e-8;const ll     mod    =   1e9+7;const ull    mx     =   133333331;struct e{    int next;    int to;}edges[MAXN];int head[MAXN];int val[MAXN];int vis[MAXN];int color_num[MAX];int cnt;int n,m;void init(){    mem(edges,0);    mem(val,0);    mem(vis,0);    mem(head,-1);    mem(color_num,0);    cnt = n = m = 0;}void addedge(int u,int v){    edges[cnt].to = v;    edges[cnt].next = head[u];    head[u] = cnt++;}void getmap(int m){    int x,y;    for(int i=1;i<=m;i++){        scanf("%d %d",&x,&y);        addedge(x,y);        addedge(y,x);    }}int Size,num;void dfs(int u){    Size++;    color_num[val[u]]++;    num = max(num,color_num[val[u]]);    for(int i=head[u];i!=-1;i=edges[i].next){        int v = edges[i].to;        if(!vis[v]){            vis[v] = 1;            dfs(v);        }    }}void dfs1(int u){    color_num[val[u]] = 0;    for(int i=head[u];i!=-1;i=edges[i].next){        int v = edges[i].to;        if(vis[v] == 1){            vis[v] = 2;            dfs1(v);        }    }}int main(){    init();    int k;    cin >> n >> m >>k;    for(int i=1;i<=n;i++) scanf("%d",&val[i]);    getmap(m);    int sum = 0;    for(int i=1;i<=n;i++){        num = Size = 0;        if(!vis[i]){            vis[i] = 1;            dfs(i);            sum += (Size - num);            vis[i] = 2;            dfs1(i);//            cout << Size << ' ' << num << ' ' << sum << endl;        }    }    cout << sum << endl;}

0 0