帶花樹演算法模板

code：

#include <iostream>
#include <string>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <cmath>
#include <queue>
#include <functional>
#include <vector>
#include <map>
#include <set>
#include <stack>
#include 
 
<fstream>
#include <sstream>
#include <unordered_map>
#define FT(a, b) memset(a, b, sizeof(a))
#define FAT(a) memset(a, 0, sizeof(a))
using namespace std;
typedef long long ll;
const int N = 1e3 + 10;
const int M = 1e5 + 100;
const int INF = 0x3f3f3f3f;
const int mod = 1e9 + 7;
int n, m, k, x, y, t;
 
int e[M], ne[M], h[N], idx;
int match[N];
int pre[N], col[N], f[N];
queue<int> q;
void add(int a, int b)
{
    e[idx] = b, ne[idx] = h[a], h[a] = idx++;
}
int find(int x)
{
    if (f[x] == x)
        return x;
    return f[x] = find(f[x]);
}
int mark = 0, dfn[N];
int lca(int a, int b)
{
    ++mark;
    a 
 
= find(a), b = find(b);
    while (dfn[a] != mark)
    {
        dfn[a] = mark;
        a = find(pre[match[a]]);
        if (b)
            swap(a, b);
    }
    return a;
}

void shrink(int a, int b, int c)
{
    while (find(a) != c)
    {
        pre[a] = b, b = match[a];
        if (col[b] == 2)
            col[b] = 1, q.push(b);
        if (find(a) == a)
            f[a] = c;
        if (find(b) == b)
            f[b] = c;
        a = pre[b];
    }
}
bool aug(int now)
{
    for (int i = 1; i <= n; ++i)
        f[i] = i, col[i] = pre[i] = 0;
    while (q.size())
        q.pop();
    q.push(now);
    col[now] = 1;
    while (q.size())
    {
        int a = q.front();
        q.pop();
        for (int i = h[a]; ~i; i = ne[i])
        {
            int j = e[i];
            if (find(a) != find(j) && col[j] != 2)
            {
                if (!col[j])
                {
                    col[j] = 2, pre[j] = a;
                    if (!match[j])
                    {
                        int x = j;
                        while (x)
                        {
                            int t = match[pre[x]];
                            match[x] = pre[x];
                            // swap(x, match[pre[x]]);
                            match[pre[x]] = x;
                            x = t;
                        }
                        return 1;
                    }
                    q.push(match[j]), col[match[j]] = 1;
                }
                else
                {
                    int c = lca(a, j);
                    shrink(a, j, c), shrink(j, a, c);
                }
            }
        }
    }
    return 0;
}
void solve()
{
    scanf("%d%d", &n, &m);
    idx = 0, FT(h, -1);
    for (int i = 0; i < m; ++i)
    {
        int a, b;
        scanf("%d%d", &a, &b);
        add(a, b), add(b, a);
    }
    int ans = 0;
    FAT(match);
    for (int i = 1; i <= n; ++i)
        if (!match[i])
            ans += aug(i);
    printf("%d\n", ans);
    for (int i = 1; i <= n; ++i)
        printf(" %d" + (i == 1), match[i]);
    puts("");
}

int main()
{
#ifdef ONLINE_JUDGE
#else
    freopen("/home/wjy/code/in.txt", "r", stdin);
    // freopen("/home/wjy/code/ans1.txt","w", stdout);
#endif
    // ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    int T = 1;
    // scanf("%d", &T);
    // cin >> T;
    // time_t begin, end;
    // begin = clock();
    while (T--)
        solve();

    // end = clock();
    // double ret = double(end - begin) / CLOCKS_PER_SEC;
    return 0;
}