POJ 3417 Network

传送门

#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>

using namespace std;
typedef long long ll;
typedef pair<int, int> p;
const int maxn(1e5 + 10);
const int maxm(2e5 + 10);
int n, m, ecnt, head[maxn];
int d[maxn], dep[maxn], f[maxn][17];

struct edge {
    int to, nxt;
} edges[maxm];

template<typename T>
inline const T read()
{
    T 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 << 3) + (x << 1) + ch - '0';
        ch = getchar();
    }
    return x * f;
}

template<typename T>
inline void write(T x, bool ln)
{
    if (x < 0) {
        putchar('-');
        x = -x;
    }
    if (x > 9) write(x / 10, false);
    putchar(x % 10 + '0');
    if (ln) putchar(10);
}

void addEdge(int u, int v)
{
    edges[ecnt].to = v;
    edges[ecnt].nxt = head[u];
    head[u] = ecnt++;
}

void bfs(int root)
{
    dep[root] = 1;
    queue<int> q;
    q.push(root);
    while (not q.empty()) {
        int u = q.front();
        q.pop();
        for (int i = head[u]; compl i; i = edges[i].nxt) {
            int v = edges[i].to;
            if (not dep[v]) {
                q.push(v);
                dep[v] = dep[u] + 1;
                f[v][0] = u;
                for (int j = 1; j < 17; ++j) {
                    f[v][j] = f[f[v][j - 1]][j - 1];
                }
            }
        }
    }
}

int lca(int u, int v)
{
    if (dep[u] < dep[v]) {
        swap(u, v);
    }
    for (int i = 16; i >= 0; --i) {
        if (dep[f[u][i]] >= dep[v]) {
            u = f[u][i];
        }
    }
    if (u == v) {
        return u;
    }
    for (int i = 16; i >= 0; --i) {
        if (f[u][i] not_eq f[v][i]) {
            u = f[u][i];
            v = f[v][i];
        }
    }
    return f[u][0];
}

int dfs(int cur, int pre, int& sum)
{
    int res = d[cur];
    for (int i = head[cur]; compl i; i = edges[i].nxt) {
        int nxt = edges[i].to;
        if (nxt not_eq pre) {
            int val = dfs(nxt, cur, sum);
            res += val;
            if (not val) {
                sum += m;
            } else if (val == 1) {
                sum += 1;
            }
        }
    }
    return res;
}

int main()
{
#ifdef ONLINE_JUDGE
#else
    freopen("input.txt", "r", stdin);
#endif
    ios::sync_with_stdio(false);
    n = read<int>();
    m = read<int>();
    memset(head, -1, sizeof head);
    for (int i = 0; i < n - 1; ++i) {
        int u = read<int>(), v = read<int>();
        addEdge(u, v);
        addEdge(v, u);
    }
    bfs(1);
    for (int i = 0; i < m; ++i) {
        int u = read<int>(), v = read<int>();
        d[u] += 1;
        d[v] += 1;
        d[lca(u, v)] -= 2;
    }
    int sum = 0;
    dfs(1, 0, sum);
    write(sum, true);
    return 0;
}