学步园

传送门：【HDU】3715 Go Deeper

题目分析：

二分能到达的深度。设对于第i层，a表示x[a[i]]取0，~a表示x[a[i]]取1，b同理。

然后按冲突建边：

c = 0 : < a , ~b > , < b , ~a >，不能同时取0

c = 1 : < a , b > , < ~b , ~a > , < b , a > , < ~a , ~b >，a、b必须取相同

c = 2 : < ~a , b > , < ~b , a >，不能同时取1

代码如下：

#include <cmath>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std ;

#define REP( i , a , b ) for ( int i = ( a ) ; i < ( b ) ; ++ i )
#define FOR( i , a , b ) for ( int i = ( a ) ; i <= ( b ) ; ++ i )
#define REV( i , a , b ) for ( int i = ( a ) ; i >= ( b ) ; -- i )
#define CLR( a , x ) memset ( a , x , sizeof a )

const int MAXN = 400 ;
const int MAXE = 40000 ;

struct Edge {
	int v ;
	Edge* next ;
} ;

struct Line {
	int x , y , c ;
} ;

Edge E[MAXE] , *H[MAXN] , *cur ;
int dfn[MAXN] , low[MAXN] , scc[MAXN] , scc_cnt ;
int S[MAXN] , top , dfs_clock ;
int n , m ;

Line l[MAXE] ;

void init () {
	cur = E ;
	top = 0 ;
	scc_cnt = 0 ;
	dfs_clock = 0 ;
	CLR ( H , 0 ) ;
	CLR ( dfn , 0 ) ;
	CLR ( scc , 0 ) ;
}

void addedge ( int u , int v ) {
	cur -> v = v ;
	cur -> next = H[u] ;
	H[u] = cur ++ ;
}

void tarjan ( int u ) {
	dfn[u] = low[u] = ++ dfs_clock ;
	S[top ++] = u ;
	for ( Edge* e = H[u] ; e ; e = e -> next ) {
		int v = e -> v ;
		if ( !dfn[v] ) {
			tarjan ( v ) ;
			low[u] = min ( low[u] , low[v] ) ;
		} else if ( !scc[v] ) low[u] = min ( low[u] , dfn[v] ) ;
	}
	if ( low[u] == dfn[u] ) {
		++ scc_cnt ;
		do {
			scc[S[-- top]] = scc_cnt ;
		} while ( u != S[top] ) ;
	}
}


void scanf ( int& x , char c = 0 ) {
	while ( ( c = getchar () ) < '0' || c > '9' ) ;
	x = c - '0' ;
	while ( ( c = getchar () ) >= '0' && c <= '9' ) x = x * 10 + c - '0' ;
}


bool ok () {
	REP ( i , 0 , n << 1 ) if ( !dfn[i] ) tarjan ( i ) ;
	REP ( i , 0 , n ) if ( scc[i << 1] == scc[i << 1 | 1] ) return 0 ;
	return 1 ;
}

void solve () {
	scanf ( "%d%d" , &n , &m ) ;
	REP ( i , 0 , m ) scanf ( l[i].x ) , scanf ( l[i].y ) , scanf ( l[i].c ) ;
	int low = 0 , high = m ;
	while ( low < high ) {
		int mid = ( low + high + 1 ) >> 1 ;
		init () ;
		REP ( i , 0 , mid ) {
			if ( l[i].c == 0 ) {
				addedge ( l[i].x << 1 , l[i].y << 1 | 1 ) ;
				addedge ( l[i].y << 1 , l[i].x << 1 | 1 ) ;
			} else if ( l[i].c == 1 ) {
				addedge ( l[i].x << 1 , l[i].y << 1 ) ;
				addedge ( l[i].y << 1 , l[i].x << 1 ) ;
				addedge ( l[i].x << 1 | 1 , l[i].y << 1 | 1 ) ;
				addedge ( l[i].y << 1 | 1 , l[i].x << 1 | 1 ) ;
			} else {
				addedge ( l[i].x << 1 | 1 , l[i].y << 1 ) ;
				addedge ( l[i].y << 1 | 1 , l[i].x << 1 ) ;
			}
		}
		if ( ok () ) low = mid ;
		else high = mid - 1 ;
	}
	printf ( "%d\n" , low ) ;
}

int main () {
	int T ;
	scanf ( "%d" , &T ) ;
	while ( T -- ) solve () ;
	return 0 ;
}