51nod 2602 树的直径

树的直径模板题

#include<iostream>
#include<stdio.h>
#include<algorithm>
#include<map>
#include<set>
#include<queue>
#include<vector>
#include<cstring>
#include<stack>

#define mem(ss) memset(ss,0,sizeof(ss))
#define rep(d, s, t) for(int d=s;d<=t;d++)
#define rev(d, s, t) for(int d=s;d>=t;d--)
#define inf 0x3f3f3f3f
typedef long long ll;
typedef long double ld;
typedef double db;
typedef std::pair<int, int> pii;
typedef std::pair<ll, ll> pll;
const ll mod = 1e9 + 7;
const int N = 1e5 + 10;
#define io_opt ios::sync_with_stdio(false);cin.tie(0);cout.tie(0)
using namespace std;

ll gcd(ll a, ll b) { return b == 0 ? a : gcd(b, a % b); }

inline ll read() {
    ll x = 0, f = 1;
    char ch = getchar();
    while (ch < '0' || ch > '9') {
        if (ch == '-')f = -1;
        ch = getchar();
    }
    while (ch >= '0' && ch <= '9') {
        x = x * 10 + ch - '0';
        ch = getchar();
    }
    return x * f;
}

ll m_pow(ll x, ll n, ll m) {
    ll res = 1;
    while (n > 0) {
        if (n & 1)
            res = (res * x) % m;
        x = (x * x) % m;
        n >>= 1;
    }
    return res % m;
}

struct Edge {
    int u, w;
};
int n, m;
int dis[N * 2];
bool vis[N];
vector<Edge> v[N];

void addEdge(int from, int to, int w) {
    v[from].push_back(Edge{to, w});
    v[to].push_back(Edge{from, w});
}

void dfs(int x) {
    vis[x] = true;
    for (auto e:v[x])
        if (!vis[e.u]) {
            dis[e.u] = dis[x] + e.w;
            dfs(e.u);
        }
}

int main() {
    scanf("%d", &n);
    m = n - 1;
    for (int i = 1; i <= m; i++) {
        int x, y;
        scanf("%d%d", &x, &y);
        addEdge(x, y, 1);
        addEdge(y, x, 1);
    }

    memset(vis, false, sizeof(vis));
    memset(dis, inf, sizeof(dis));
    dis[1] = 0;
    dfs(1);

    int start, endd, maxx = -inf;
    for (int i = 1; i <= n; i++)
        if (dis[i] > maxx && dis[i] != inf) {
            maxx = dis[i];
            start = i;
        }

    memset(vis, false, sizeof(vis));
    memset(dis, inf, sizeof(dis));
    dis[start] = 0;
    dfs(start);

    maxx = -inf;
    for (int i = 1; i <= n; i++)
        if (dis[i] > maxx && dis[i] != inf) {
            maxx = dis[i];
            endd = i;
        }
    cout << maxx;
    return 0;
}