1811 Rank of Tetris

#include<iostream>
#include<cstdio>
#include<algorithm>

using namespace std;

int father[10001]; 

void clean_father(int n)
{
    for (int i=0;i<n;i++) father[i]=i;
} 

int getfather(int x)
{
    if (father[x]!=x) father[x]=getfather(father[x]);
    return father[x];
}

void link(int x,int y)
{
    father[getfather(x)]=getfather(y);
} 

int x[20001],y[20001],rd[10001],num[10001],start[10001];
char z[20001];

typedef struct {
    int a,b;
} node;
node a[20001];

bool op(node a,node b)
{
    return a.a<b.a;
}

int stack[10001];

int main()
{
    int n,m;
    while (scanf("%d%d",&n,&m)!=EOF)
    {
        clean_father(n);
        
        for (int i=1;i<=m;i++)
        {
            scanf("%d %c %d",&x[i],&z[i],&y[i]);
            if (z[i]==‘=‘) link(x[i],y[i]);
        }
        
        int tail=0;
        for (int i=0;i<n;i++) rd[i]=-1;
        int tot=0;
        for (int i=0;i<n;i++) 
        {
            rd[getfather(i)]=0;
            if (rd[i]==0) tot++;
        }
        for (int i=1;i<=m;i++)
        switch(z[i])
        {
            case ‘>‘:
                tail++;
                a[tail].a=getfather(x[i]);
                a[tail].b=getfather(y[i]);
                rd[getfather(y[i])]++;
                break;
            case ‘<‘:
                tail++;
                a[tail].a=getfather(y[i]);
                a[tail].b=getfather(x[i]);
                rd[getfather(x[i])]++;
        }
        sort(&a[1],&a[tail+1],op);
        
        int o=-1;
        for (int i=0;i<n;i++) num[i]=0;
        for (int i=1;i<=tail;i++)
        {
            if (a[i].a!=o)
            {
                o=a[i].a;
                start[o]=i;
            }
            num[o]++;
        }
        
        int top=0;
        for (int i=0;i<n;i++)
        if (rd[i]==0)
        {
            top++;
            stack[top]=i;
        }
        
        if (top==0)
        {
            printf("CONFLICT\n");
            continue;
        }
        
        bool flag=false,done=false;
        while (top>0&&(!done))
        {
            if (top>1) flag=true;
            int now=stack[top];
            top--;tot--;
            for (int i=0;i<num[now];i++)
            {
                rd[a[start[now]+i].b]--;
                if (rd[a[start[now]+i].b]==0) 
                {
                    top++;
                    stack[top]=a[start[now]+i].b;
                } else
                if (rd[a[start[now]+i].b]<0)
                {
                    done=true;
                    break;
                }
            }
            num[now]=0;
        }
        if (tot>0||done) printf("CONFLICT\n");
        else if (flag) printf("UNCERTAIN\n");
        else printf("OK\n");
    }
    
    return 0;
}