星球大战

洛谷-P1197-星球大战

分析

离线+倒序处理。

实现

#include <iostream>
#include <cstring>
using namespace std;

const int N = 800010;
struct edge {
    int to, next;
};
edge e[2 * 2 * N];
int idx, head[N];
int n, m, k;
int a[N];
bool mark[N];
int f[N];
int res[N];

void add_edge (int u, int v) {
    e[idx].to = v;
    e[idx].next = head[u];
    head[u] = idx ++;
}
int find (int x) {
    if (f[x] == x) return x;
    return f[x] = find(f[x]);
}
void merge (int x, int y) {
    f[find(x)] = find(y);
}
bool query (int x, int y) {
    return find(x) == find(y);
}

int main () {
    memset(head, -1, sizeof(head));
    scanf("%d%d", &n, &m);
    for (int i = 1, u, v; i <= m; ++ i) {
        scanf("%d%d", &u, &v);
        ++ u, ++ v;
        add_edge(u, v);
        add_edge(v, u);
    }
    scanf("%d", &k);
    for (int i = 1; i <= k; ++ i) {
        scanf("%d", &a[i]);
        mark[++ a[i]] = true; // 摧毁
    }

    for (int i = 1; i <= n; ++ i) f[i] = i;
    int cnt = 0; // 连通块数
    for (int i = 1; i <= n; ++ i) {
        if (mark[i] == true) continue;
        for (int j = head[i]; j != -1; j = e[j].next) {
            int to = e[j].to;
            if (mark[to] == true) continue;
            merge(i, to);
        }
    }
    for (int i = 1; i <= n; ++ i)
        cnt += (f[i] == i && mark[i] == false);
    
    for (int i = k; i >= 1; -- i) { // 倒序处理
        res[i] = cnt;
        mark[a[i]] = false;
        ++ cnt;
        for (int j = head[a[i]]; j != -1; j = e[j].next) {
            int to = e[j].to;
            if (mark[to] == false && query(a[i], to) == false) {
                merge(a[i], to);
                -- cnt;
            }
        }
    }
    res[0] = cnt;
    for (int i = 0; i <= k; ++ i)
        printf("%d\n", res[i]);
    return 0;
}