2023-8-28 树的重心(树与图的深度优先遍历)

题目链接：树的重心

#include 
#include 
#include 

using namespace std;

const int N = 100010, M = N * 2;

int n;
int h[N], e[M], ne[M], idx;
int ans = N;
bool st[N];

void add(int a, int b)
{
    e[idx] = b, ne[idx] = h[a], h[a] = idx ++;
}

// 以u为根的子树中点的数量(包含u)
int dfs(int u)
{
    // 记录当前点已经查找过了
    st[u] = true;
    
    int sum = 0, size = 0;
    for(int i = h[u]; i != -1; i = ne[i])
    {
        int j = e[i];
        if(!st[j])
        {
            int s = dfs(j);
            size = max(size, s);
            sum += s;
        }
    }
    size = max(size, n - sum - 1);
    ans = min(size, ans);
    return sum + 1;
}

int main()
{
    cin >> n;
    memset(h, -1, sizeof h);
    for(int i = 0; i < n -1; i++)
    {
        int a, b;
        cin >> a >> b;
        add(a, b), add(b, a);
    }
    dfs(1);
    cout << ans << endl;
    return 0;
}