Uvalive 4262--trip Planning —————— "Tarjan to find the number of strong connected components"

Road NetworksTime limit:3000MS Memory Limit:0KB 64bit IO Format:%lld &%llu SubmitStatusPracticeuvalive 4262

Description

There is a road network comprised byM<tex2html_verbatim_mark> Roads andN<tex2html_verbatim_mark> cities. For convenience, we use{1, 2,...,N}<tex2html_verbatim_mark> to denote theN<tex2html_verbatim_mark> cities. Each road between citiesI<tex2html_verbatim_mark> andJ<tex2html_verbatim_mark>, where1I<tex2html_verbatim_mark>,JN<tex2html_verbatim_mark> andIJ<tex2html_verbatim_mark>, has both types:one type isBidirectional, which allows a citizen to drive a car from i <tex2html_verbatim_mark> to  J < tex2html_verbatim_mark>  (denoted By  i J <tex2html_verbatim_ mark> ) and From  J <tex2html_verbatim_mark> to  i <tex2html_verbatim_mark>  (denoted By  J I <tex2html_verbatim_mark> ). The other type Is unidirectional, which allows a citizen to drive a car following exactly one di Rection, either From  i <tex2html_verbatim_mark> to  J <tex2html_verbatim_mark> or from  J < Tex2html_verbatim_mark> to  i <tex2html_verbatim_mark> .

We say that cityJ<tex2html_verbatim_mark> isReachable from cityI<tex2html_verbatim_mark> if one can drive a car fromI<tex2html_verbatim_mark> toJ<tex2html_verbatim_mark>, visiting a sequence of citiesC1,C2,...,CK<tex2html_verbatim_mark> fork0<tex2html_verbatim_mark>, such thatIC1C2 ...CKJ<tex2html_verbatim_mark>. (Every city was always reachable from itself.) Aregion is a maximal set of cities So, the following  mutually reachable property holds:for both arbitrary cities  i <tex2html_verbatim_mark> and  J <tex2html_verbatim_mark > ,  i <tex2html_verbatim_mark> is reachable From  J <tex2html_verbatim_mark> and  J <tex2html_ Verbatim_mark> is also reachable From  i <tex2html_verbatim_mark>  . The adjective "maximal" means that if we include any and the given region, the mutually reachable property cann OT be retained. Given a road network, your task is to write a computer program to compute the number of regions in the road Network.

Technical specification

2. We use {1, 2,..., n}<tex2html_verbatim_mark> to denote the n<tex2html_verbatim_mark > Cities.
4. M2000<tex2html_verbatim_mark> is a non-negative integer
6. N1000<tex2html_verbatim_mark> is a positive integer.
7. If a road betweenI<tex2html_verbatim_mark> andJ<tex2html_verbatim_mark> is bidirectional, then we use the order pairs(I,J) <tex2html_verbatim_mark> and(J,I) <tex2html_verbatim_mark> to represent it. Otherwise, if a road between i<tex2html_verbatim_mark>and J<tex2html_verbatim_mark> is unidirectional From i<tex2html_verbatim_mark> to J<tex2html_verbatim_mark> (respectively, J<tex2html_verbatim_mark> to i<tex2html_verbatim_mark>), we use (  i<tex2html_verbatim_mark>, J<tex2html_verbatim_mark>) (respectively, ( J<tex2html_verbatim_mark>, i<tex2html_verbatim_mark>) to represent it .

Input

The input consists of a number of test cases. The first line of the input file contains a integer indicating the number of the test cases to follow. Each test case consists of a road network, which have the following format:the first line of all test case contains n umbers,  N <tex2html_verbatim_mark>and  M <tex2html_ verbatim_mark>  separated by a single space. The Next  M <tex2html_verbatim_mark> lines contain the description of   M <tex2html_verbatim_mark> roads such that one, line contains, cities Representing an order Pair  i ,   J ) <tex2html_verbatim_mark>  . Each of the line are represented by and positive numbers separated by a single space; The first number representing the former element in the order pair and the second number representing the latter element I n the order pair. A '   0 ' at The  M + 2) <tex2html_verbatim_mark> -th line of Each test case, except for the last Test case, indicates the end of this test case.

The next test case starts after the previous ending symbol '0'. Finally, a '-1' signals the end of the whole inputs.

Output

The output contains one line for each test case. Each line contains a integer, which is the number of the regions in the given road network.

Sample Input

2 3 21 21 30 3 31 22 33 1-1

Sample Output

3 1



The main topic: give you n points, M Bar has an edge. Ask you the number of SCC in this diagram.

Problem-solving ideas: To find strong connected components of the template problem, Tarjan algorithm water over.

/* Tarjan number of strongly connected components */#include <stdio.h> #include <algorithm> #include <string.h> #include <stack > #include <vector> #include <queue>using namespace std;const int maxn = 1E5+200;VECTOR&LT;INT&GT;G[MAXN] ; int pre[maxn],lowlink[maxn],sccno[maxn],dfs_clock,scc_cnt;stack<int>s;void dfs (int u) {pre[u] = Lowlink[u] = + +    Dfs_clock;    S.push (U);        for (int i = 0;i < G[u].size (); i++) {int v = g[u][i];            if (!pre[v]) {DFS (v);        Lowlink[u] = min (Lowlink[u], lowlink[v]);        }else if (!sccno[v]) {Lowlink[u] = min (Lowlink[u], pre[v]);        }} if (lowlink[u] = = Pre[u]) {scc_cnt++; for (;;) {int x = S.top ();            S.pop ();            SCCNO[X] = scc_cnt;        if (x = = u) break;    }}}void FIND_SCC (int n) {dfs_clock = scc_cnt = 0; while (!    S.empty ()) S.pop ();    memset (sccno, 0, sizeof (SCCNO));    memset (pre, 0, sizeof (pre)); for (int i = 1; I <= n; i++) {if (!pre[i]) DFS (i);    }}int Main () {int t,n,m;    scanf ("%d", &t);        while (t--) {scanf ("%d%d", &n,&m);        int A, B;            for (int i = 0; i < m; i++) {scanf ("%d%d", &a,&b);        G[a].push_back (b);        } scanf ("%d", &a);        FIND_SCC (n);        printf ("%d\n", scc_cnt);        for (int i = 0; I <= N; i++) {g[i].clear (); }} return 0;}

　　

Uvalive 4262--trip Planning —————— "Tarjan to find the number of strong connected components"