C :

#include <stdio.h>
#include <stdlib.h>

int f[40005];

int getindex(int x, int y, int n){
return (x-1) * n + y;
}

int find(int v){
if(f[v] == v)return v;
int F = find(f[v]);
f[v] = F;
return F;
}

int main()
{
    int n, m;
    while(scanf("%d%d",&n,&m) != EOF){
        for(int i = 1;i <= n * n; i++)f[i] = i;
        int flag = 1;
        for(int j = 1;j <= m; j++){
            int x, y;
            char op;
            scanf("%d %d %c",&x,&y,&op);
            getchar();
            int index1 = getindex(x, y, n);
            int index2 = op=='D'?getindex(x+1,y, n):getindex(x,y+1, n);
            int f1 = find(index1);
            int f2 = find(index2);
            if(f1 != f2)f[f1] = f2;
            else{
                if(flag){
                  printf("%d\n",j);
                  flag = 0;
                  return 0;
                }
            }
        }
        if(flag)printf("draw\n");
    }
    return 0;
}

C++ :

#include<iostream>
#include<cstdio>
using namespace std;
struct node
{
	int x,y;
}f[301][301],k1,k2;
int i,j,m,n,x,y;
char c;
node root(node k)
{
	if((f[k.x][k.y].x==k.x)&&(f[k.x][k.y].y==k.y))return k;
	f[k.x][k.y]=root(f[k.x][k.y]);
	return f[k.x][k.y];
}
int main()
{
	cin>>n>>m;
	for(i=1;i<=n;i++)
	{
		for(j=1;j<=n;j++)
		{
			f[i][j].x=i;
			f[i][j].y=j;
		}
	}
	for(i=1;i<=m;i++)
	{
		cin>>x>>y>>c;
		if(c=='D')
		{
			k1=root(f[x][y]);
			k2=root(f[x+1][y]);
		}
		if(c=='R')
		{
			k1=root(f[x][y]);
			k2=root(f[x][y+1]);
		}
		if((k1.x==k2.x)&&(k1.y==k2.y))
		{
			cout<<i<<endl;
			return 0;
		}
		else f[k1.x][k1.y]=k2;
	}
	cout<<"draw"<<endl;
	return 0;
}