技術標籤：強連通

如果葉子數(縮點後度為1的點)為1，則至少需要新增0條邊；
否則為（葉子數+1）/ 2;

#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stack>
#define mem(a,b) memset(a,b,sizeof(a))
const int N = 202000;
typedef long long ll;
using namespace std;
struct node
{
    int u, v, net;
} e[N];
int head[
 
N], tot, pre[N];
void add(int u, int v)
{
    e[++tot].v = v;
    e[tot].u = u;
    e[tot].net = head[u];
    head[u] = tot;
}
int dfn[N], low[N], cnt, s[N], tp;
int scc[N], sc;
int sz[N], n, m, out[N];
void tarjan(int u, int f)
{
    low[u] = dfn[u] = ++cnt;
    pre[u] = f;
    s[++tp] = u;

    for
 
 (int i = head[u]; i; i = e[i].net)
    {
        int v = e[i].v;

        if (v == f)
            continue;

        if (!dfn[v])
        {
            tarjan(v, u);
            low[u] = min(low[u], low[v]);
        }
        else
            low[u] = min(low[u], dfn[v]);
    }

    if (dfn[u] == low[
 
u])
    {
        ++sc;

        while (s[tp] != u)
        {
            scc[s[tp]] = sc;
            --tp;
        }

        scc[s[tp]] = sc, --tp;
    }
}
int main()
{
    scanf("%d%d", &n, &m);

    for (int i = 1; i <= m; i++)
    {
        int u, v;
        scanf("%d%d", &u, &v);
        add(u, v);
        add(v, u);
    }

    // printf("---\n");
    for (int i = 1; i <= n; i++)
    {
        if (!dfn[i])
            tarjan(i, i);
    }

    for (int u = 1; u <= n; u++)
    {
        if (scc[u] != scc[pre[u]])
        {
            sz[scc[u]]++;
            sz[scc[pre[u]]]++;
        }
    }

    int ans = 0;

    for (int i = 1; i <= sc; i++)
    {
        if (sz[i] == 1)
            ans++;
    }

    printf("%d\n", (ans + 1) >> 1);
    return 0;
}