UVA10765-Doves and bombs (BCC)

Question Link

Given an undirected graph of N points, the "Pigeon value" of a point is defined as the number of connected blocks after it is deleted. Find the first m in descending order of "Pigeon value.

Train of Thought: in fact, the question is to find the top cut, we only need to find the top cut, and then record that the top cut belongs to several public points of different connected components, not cut points. after removal, the number of connected parts of the graph is 1.

Code:

#include <iostream>#include <cstdio>#include <cstring>#include <vector>#include <stack>#include <algorithm>using namespace std;const int MAXN = 10005;struct node{    int id, val;}b[MAXN];int n, m;int pre[MAXN], low[MAXN], dfs_clock;vector<int> g[MAXN];void init() {    for (int i = 0; i < n; i++)         g[i].clear();    for (int i = 0; i < n; i++) {        b[i].id = i;         b[i].val = 1;    }     }bool cmp(node a, node b) {    if (a.val == b.val)        return a.id < b.id;    return a.val > b.val;}int dfs(int u, int fa) {    int lowu = pre[u] = ++dfs_clock;    int child = 0;    for (int i = 0; i < g[u].size(); i++) {        int v = g[u][i];         if (!pre[v]) {            child++;            int lowv = dfs(v, u);            lowu = min(lowu, lowv);            if (lowv >= pre[u]) {                b[u].val++;            }        }         else if (pre[v] < pre[u] && v != fa) {            lowu = min(lowu, pre[v]);        }    }    if (fa < 0 && child == 1) b[u].val = 1;    low[u] = lowu;    return lowu;}void find_bcc(int n) {    memset(pre, 0, sizeof(pre));    memset(low, 0, sizeof(low));    dfs_clock = 0;    for (int i = 0; i < n; i++)        if (!pre[i])            dfs(i, -1);}int main() {    while (scanf("%d%d", &n, &m)) {        if (n == 0 && m == 0)            break;        init();        int u, v;        while (scanf("%d%d", &u, &v)) {            if (u == -1 && v == -1)                break;            g[u].push_back(v);            g[v].push_back(u);         }        find_bcc(n);        sort(b, b + n, cmp);        for (int i = 0; i < m; i++)            printf("%d %d\n", b[i].id, b[i].val);        puts("");    }         return 0;}

UVA10765-Doves and bombs (BCC)