Tarjan poj1236 poj2186 of SCC

Both questions are water questions. 1236 the first question is the number of points with a degree of 0 after the contraction point. The second question is how many sides are added to make the full graph strongly connected. This is a classic practice, read white books for details

Poj2186 is the number of points (the number of points in SCC) included in the unique vertex with a contraction degree of 0)

//poj1236

#include<iostream>

#include<cstdio>

#include<string.h>

#define maxn 6000

int now=0,next[maxn],head[maxn],point[maxn],num=0,dfn[maxn],low[maxn],instack[maxn];

int stack[maxn],belong[maxn],top,count,in[maxn],out[maxn];

int min(int a,int b)

{

    if (a<b)return a;else return b;

}

int max(int a,int b)

{

    if (a>b)return a;else return b;

}

void add(int x,int y)

{

    next[++now]=head[x];

    head[x]=now;

    point[now]=y;

}

void tarjan(int k)

{

    int u;

    instack[k]=true;

    dfn[k]=low[k]=++num;stack[++top]=k;

    for(int i=head[k];i!=0;i=next[i])

    {

        u=point[i];

        if (dfn[u]==0)

        {

            tarjan(u);

            low[k]=min(low[k],low[u]);

        }

        else if (instack[u])low[k]=min(dfn[u],low[k]);

    }

    if (low[k]==dfn[k])

    {

        ++count;

        do

        {

            u=stack[top--];

            instack[u]=false;

            belong[u]=count;

        }while(u!=k);

    }

}

int main()

{

    int n,t;

    scanf("%d",&n);

    for(int i=1;i<=n;i++)while (1)

    {

        scanf("%d",&t);

        if (t==0)break;

        else add(i,t);

    }

    for(int i=1;i<=n;i++)if (dfn[i]==0)tarjan(i);

    for(int i=1;i<=n;i++)

    {

        for(int j=head[i];j!=0;j=next[j])

        {

            int u=point[j];

            if (belong[i]!=belong[u])

            {

                out[belong[i]]++;

                in[belong[u]]++;

            }

        }

    }

    int countout=0,countin=0;

    for(int i=1;i<=count;i++)

    {

        if (out[i]==0)countout++;

        if (in[i]==0)countin++;

    }

    if (count==1)printf("1\n0\n");

    else printf("%d\n%d\n",countin,max(countout,countin));

    return 0;

}

// Poj2186

# Include <iostream>

# Include <cstdio>

# Include <string. h>

# Define maxn50010

Using namespace STD;

Intnow = 0, next [maxn], head [maxn], point [maxn], num = 0, dfn [maxn], low [maxn], instack [maxn];

Int stack [maxn], belong [maxn], top, Count, out [maxn], p [maxn];

Void add (int x, int y)

{

Next [++ now] = head [x];

Head [x] = now;

Point [now] = y;

}

Void Tarjan (int K)

{

Instack [k] = 1;

Stack [++ top] = K;

Low [k] = dfn [k] = ++ num;

Int U;

For (INTI = head [k]; I! = 0; I = next [I])

{

U = point [I];

If (dfn [u] = 0)

{

Tarjan (U );

Low [k] = min (low [u], low [k]);

}

Else if (instack [u] = 1) low [k] = min (dfn [u], low [k]);

}

If (low [k] = dfn [k])

{

++ Count;

Do

{

U = stack [top --];

Instack [u] = 0;

Belong [u] = count;

P [count] ++;

} While (u! = K );

}

}

 

Int main ()

{

Int n, m, X, Y, ANS = 0;

Scanf ("% d", & N, & M );

For (INT I = 1; I <= m; I ++)

{

Scanf ("% d", & X, & Y );

Add (x, y );

}

For (INT I = 1; I <= N; I ++)

If (dfn [I] = 0) Tarjan (I );

For (INT I = 1; I <= N; I ++)

{

For (Int J = head [I]; J! = 0; j = next [J])

{

Int u = point [J];

If (belong [I]! = Belong [u]) out [belong [I] ++;

}

}

Int flag = 0;

For (INTI = 1; I <= count; I ++)

{

If (ANS! = 0 & out [I] = 0) {flag = 1; break ;}

If (out [I] = 0) ans = P [I];

}

If (flag = 0) printf ("% d \ n", ANS); else printf ("0 \ n ");

Return 0;

}

Tarjan poj1236 poj2186 of SCC