【tarjan+lca】有机化学之神偶尔会做作弊

P2783 有机化学之神偶尔会做作弊

我觉得我对的一比可就是wa三个点我决定不改了毕竟我已经领会到精髓了

（还有这种人？？？？？

就是tarjan缩点+倍增求lca

因为是无向图，要判断一下， dfs的时候不能返回上一个点，否则全图就是一整个强连通分量了qwq

  1 #include<cmath>
  2 #include<cstdio>
  3 #include<iostream>
  4 using namespace std;
  5 const int maxn = 10010, maxm = 50050;
  6 int n, m, q, log2n, num = 0, cot = 0, top = 0, tim = 0;
  7 int head[maxm], hear[maxm], dep[maxn], sd[maxn], jump[maxn][23], sta[maxn], low[maxn], dfn[maxn], x[maxm], y[maxm];
  8 bool vis[maxn];
  9 struct edg {
 10     int nxt, to;
 11 }e[maxm << 1], edge[maxm << 1];
 12 void add(int from, int to) {
 13     e[++num].to = to;
 14     e[num].nxt = head[from];
 15     head[from] = num;
 16 }
 17 void readd(int from, int to) {
 18     edge[++cot].to = to;
 19     edge[cot].nxt = hear[from];
 20     hear[from] = cot;
 21 }
 22 void tarjan(int u, int fa) {
 23     low[u] = dfn[u] = ++tim;
 24     sta[++top] = u;
 25     vis[u] = 1;
 26     for(int i = head[u]; i; i = e[i].nxt) {
 27         int v = e[i].to;
 28         if(v != fa) {
 29             if(!dfn[v]) 
 30             {
 31                 tarjan(v, u);
 32                 low[u] = min(low[u], low[v]);
 33             }
 34             else if(vis[v]) low[u] = min(low[u], dfn[v]);
 35         }
 36     }
 37     if(dfn[u] == low[u]) {
 38         int y;
 39         while(y = sta[top--]) {
 40             sd[y] = u;
 41             vis[y] = 0;
 42             if(y == u) break;
 43         }
 44     }
 45 }
 46 void dfs(int x) {
 47     for(int i = hear[x]; i; i = edge[i].nxt) 
 48     {
 49         int y = edge[i].to;
 50         if(y != jump[x][0]) 
 51         {
 52             dep[y] = dep[x] + 1;
 53             jump[y][0] = x;
 54             dfs(y);
 55         }
 56     }
 57 }
 58 void init() {
 59     for(int i = 1; i <= log2n; i++)
 60         for(int j = 1; j <= n; j++)
 61             jump[j][i] = jump[jump[j][i-1]][i-1];
 62 }
 63 int LCA(int x, int y) {
 64     if(dep[x] < dep[y]) swap(x, y);
 65     int t = dep[x] - dep[y];
 66     for(int i = 0; (1<<i) <= n; i++) 
 67         if(t & (1<<i)) x = jump[x][i];
 68     if(x == y) return x;
 69     for(int i = log2n; i >= 0; i--)    {
 70         if(jump[x][i] != jump[y][i]) {
 71             x = jump[x][i];
 72             y = jump[y][i];
 73         }
 74     }
 75     return jump[x][0];
 76 }
 77 void print(int ans) {
 78     if (!ans) return;
 79     print(ans >> 1);
 80     printf("%d", ans & 1);
 81 }
 82 int main() {
 83     scanf("%d%d", &n, &m);
 84     log2n = log(n) / log(2) + 1;
 85     for(int i = 1; i <= m; i++) {
 86         int u, v;
 87         scanf("%d%d", &x[i], &y[i]);
 88         add(x[i], y[i]), add(y[i], x[i]);
 89     }
 90     for(int i = 1; i <= n; i++)
 91         if(!dfn[i]) tarjan(i, i);
 92     for(int i = 1; i <= m; i++) {
 93         if(sd[x[i]] != sd[y[i]]){
 94             readd(sd[x[i]], sd[y[i]]), readd(sd[y[i]], sd[x[i]]);
 95         }
 96     }
 97     jump[1][0] = 0;
 98     dep[1] = 1;
 99     dfs(1);
100     init();
101     scanf("%d", &q);
102     for(int i = 1; i <= q; i++) {
103         int u, v;
104         scanf("%d%d", &u, &v);
105         int lca = LCA(u, v);
106         int ans = dep[u] + dep[v] - 2*dep[lca] + 1;
107         print(ans);
108         printf("
");
109     }
110     return 0;
111 }