CH24C 逃不掉的路

edcc缩点之后跳倍增lca
丢个edcc缩点模板

Code:

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

const int N = 1e5 + ;
const int M = 2e5 + ;
const int Lg = ;

int n, m, qn, tot = , head[N], dep[N], fa[N][Lg];
int dfsc = , dcc = , dfn[N], low[N], bel[N], ex[M], ey[M];
bool bri[M << ], vis[N];

struct Edge {
    int to, nxt;
} e[M << ];

inline void add(int from, int to) {
    e[++tot].to = to;
    e[tot].nxt = head[from];
    head[from] = tot;
}

inline void read(int &X) {
    X = ;
    char ch = ;
    int op = ;
    for(; ch > ''|| ch < ''; ch = getchar())
        if(ch == '-') op = -;
    for(; ch >= '' && ch <= ''; ch = getchar())
        X = (X << ) + (X << ) + ch - ;
    X *= op;
}

inline int min(int x, int y) {
    return x > y ? y : x;
}

void tarjan(int x, int inEdge) {
    dfn[x] = low[x] = ++dfsc;
    for(int i = head[x]; i; i = e[i].nxt) {
        int y = e[i].to;
        if(!dfn[y]) {
            tarjan(y, i);
            low[x] = min(low[x], low[y]);
            if(dfn[x] < low[y]) bri[i] = bri[i ^ ] = ;
        } else if(i != (inEdge ^ ))
            low[x] = min(low[x], dfn[y]);
    }
}

void dfs(int x) {
    bel[x] = dcc;
    for(int i = head[x]; i; i = e[i].nxt) {
        int y = e[i].to;
        if(bel[y] || bri[i]) continue;
        dfs(y);
    }
}

void dfs2(int x, int fat, int depth) {
    vis[x] = , fa[x][] = fat, dep[x] = depth;
    for(int i = ; i <= ; i++)
        fa[x][i] = fa[fa[x][i - ]][i - ];
    for(int i = head[x]; i; i = e[i].nxt) {
        int y = e[i].to;
        if(vis[y]) continue;
        dfs2(y, x, depth + );
    }
}

void swap(int &x, int &y) {
    int t = x;
    x = y;
    y = t;
}

inline int getLca(int x, int y) {
    if(dep[x] < dep[y]) swap(x, y);
    for(int i = ; i >= ; i--)
        if(dep[fa[x][i]] >= dep[y])
            x = fa[x][i];
    if(x == y) return x;
    for(int i = ; i >= ; i--)
        if(fa[x][i] != fa[y][i])
            x = fa[x][i], y = fa[y][i];
    return fa[x][];
}

int main() {
    read(n), read(m);
    for(int i = ; i <= m; i++) {
        read(ex[i]), read(ey[i]);
        add(ex[i], ey[i]), add(ey[i], ex[i]);
    }

    for(int i = ; i <= n; i++)
        if(!dfn[i]) tarjan(i, );
    for(int i = ; i <= n; i++)
        if(!bel[i]) {
            ++dcc;
            dfs(i);
        }

/*    for(int i = 1; i <= n; i++)
        printf("%d ", bel[i]);
    printf("\n");   */

    tot = ;
    memset(head, , sizeof(head));
    for(int i = ; i <= m; i++) {
        if(bel[ex[i]] == bel[ey[i]]) continue;
        add(bel[ex[i]], bel[ey[i]]), add(bel[ey[i]], bel[ex[i]]);
    }
    for(int i = ; i <= n; i++)
        if(!vis[i]) dfs2(i, , );

    read(qn);
    for(int x, y; qn--; ) {
        read(x), read(y);
        x = bel[x], y = bel[y];
        if(x == y) puts("");
        else printf("%d\n", dep[x] + dep[y] -  * dep[getLca(x, y)]);
    }
    return ;
}