POJ1987(树分治)

k的值很大答案应该用long long。

#include <cstdio>#include <cstring>#include <algorithm>#include <iostream>#include <cmath>using namespace std;#define maxn 111111#define maxm 211111#define INF 11111111#define size Sizestruct node {    int from, to, next;    long long w;}edge[maxm];int n, m, k, cnt, root;long long ans;int head[maxn];bool vis[maxn];int size[maxn], num[maxn]; //以i为根的子树的节点 i的子树中最多的节点long long d[maxn], Min;void add_edge (int from, int to, int w) {    edge[cnt].from = from, edge[cnt].to = to, edge[cnt].w = w, edge[cnt].next = head[from],    head[from] = cnt++;}void dfs_size (int u, int fa) {    size[u] = 1;    num[u] = 0;    for (int i = head[u]; i != -1; i = edge[i].next) {        int v = edge[i].to;        if (v == fa || vis[v])            continue;        dfs_size (v, u);        size[u] += size[v];        if (size[v] > num[u]) {            num[u] = size[v];        }    }}void find_root (int u, int fa, int pre) { //找到重心    long long cur = 0;    cur = max (num[u], size[pre]-size[u]);    if (cur < Min) {        Min = cur;        root = u;    }    for (int i = head[u]; i != -1; i = edge[i].next) {        int v = edge[i].to;        if (v == fa || vis[v])            continue;        find_root (v, u, pre);    }}int tmp[maxn], tot;void get_dis (int u, int fa, int dis) { //得到每个点到当前根的距离    tmp[tot++] = dis;    for (int i = head[u]; i != -1; i = edge[i].next) {        int v = edge[i].to;        if (vis[v] || v == fa)            continue;        d[v] = dis+edge[i].w;        get_dis (v, u, d[v]);    }}int solve (int u, int d) {    long long ans = 0;    tot = 0;    get_dis (u, 0, d);    sort (tmp, tmp+tot);    int r = tot-1, l = 0;    while (r>l) {        for (; tmp[r]+tmp[l] > k && r > l; r--) {}        ans += r-l;        l++;    }    return ans;}void dfs (int u) {    Min = INF;    dfs_size (u, 0);    find_root (u, 0, u);    vis[root] = 1;    ans += solve (root, 0);    for (int i = head[root]; i != -1; i = edge[i].next) {        int v = edge[i].to;        if (vis[v])            continue;        ans -= solve (v, edge[i].w);        dfs (v);    }}int main () {    //freopen ("in", "r", stdin);    while (scanf ("%d%d", &n, &m) == 2) {        cnt = ans = 0;        int u, v, w;        char op[10];        memset (head, -1, sizeof head);        for (int i = 1; i < n; i++) {            scanf ("%d%d%d%s", &u, &v, &w, &op);            add_edge (u, v, w);            add_edge (v, u, w);        }        scanf ("%d", &k);        memset (vis, 0, sizeof vis);        dfs (1);        printf ("%lld\n", ans);    }    return 0;}