codeforces 731C (并查集 水)

题目链接：点击这里

题意：给出n只袜子的颜色，每天选择两只袜子，每次能把一只袜子染色。问最少染色几只袜子能使的每天的袜子颜色一样。

给每天穿的两只袜子连边，很显然一个分量的袜子要一起考虑，并查集维护分量就好了。然后搜出最多的颜色，把分量的点都染成这个颜色即可。

#include 
#include 
#include 
#include 
#include 
#include 
using namespace std;
#define maxn 200005

int fa[maxn], color[maxn];
#define find Find
int find (int x) {
    return fa[x] == x ? fa[x] : fa[x] = find (fa[x]);
}
int n, m, k;
vector <int> a[maxn];
int num[maxn];

int main () {
    cin >> n >> m >> k;
    for (int i = 0; i <= k; i++) a[i].clear ();
    for (int i = 1; i <= n; i++) cin >> color[i], fa[i] = i;
    for (int i = 0; i < m; i++) {
        int u, v;
        cin >> u >> v;
        int p1 = find (u), p2 = find (v);
        if (p1 != p2) {
            fa[p1] = p2;
        }
    }
    for (int i = 1; i <= n; i++) {
        a[find (i)].push_back (i);
    }
    memset (num, 0, sizeof num);
    int ans = 0;
    for (int i = 1; i <= n; i++) {
        int sz = a[i].size (), Max = 0;
        for (int j = 0; j < sz; j++) {
            int id = a[i][j];
            num[color[id]]++;
            Max = max (Max, num[color[id]]);
        }
        ans += sz-Max;
        for (int j = 0; j < sz; j++) {
            int id = a[i][j];
            num[color[id]]--;
        }
    }
    cout << ans << "\n";
    return 0;
}