二分+2SAT zoj3422 Go Deeper

传送门：点击打开链接

题意：

go(int dep, int n, int m)

begin

output the value of dep.

if dep < m and x[a[dep]] + x[b[dep]] != c[dep] then go(dep + 1, n, m)

end

然后告诉你a，b，c三个数组的值，x数组里的值只有0和1，c里只有0，1，2问最多会输出什么。

思路：我们二分最后输出的答案，然后每次check都去建边跑2SAT，看是否符合要求。

#include <map>
#include <set>
#include <cmath>
#include <ctime>
#include <stack>
#include <queue>
#include <cstdio>
#include <cctype>
#include <bitset>
#include <string>
#include <vector>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <functional>
#define fuck(x) cout<<"["<<x<<"]";
#define FIN freopen("input.txt","r",stdin);
#define FOUT freopen("output.txt","w+",stdout);
//#pragma comment(linker, "/STACK:102400000,102400000")
using namespace std;
typedef long long LL;
typedef pair<int, int> PII;

const int MX = 1e3 + 5;
const int INF = 0x3f3f3f3f;
const int mod = 1e9 + 7;

struct Edge {
int v, nxt;
} E[100005];
int Head[MX][2], erear;
void edge_init() {
erear = 0;
memset(Head, -1, sizeof(Head));
}
void edge_add(int z, int u, int v) {
E[erear].v = v;
E[erear].nxt = Head[u][z];
Head[u][z] = erear++;
}
void edge_add(int u, int v) {
edge_add(0, u, v);
edge_add(1, v, u);
}
int Stack[MX], Belong[MX], vis[MX], ssz, bsz;
void DFS(int u, int s) {
vis[u] = 1;
if(s) Belong[u] = s;
for(int i = Head[u][s > 0]; ~i; i = E[i].nxt) {
int v = E[i].v;
if(!vis[v]) DFS(v, s);
}
if(!s) Stack[++ssz] = u;
}
void tarjan(int n) {
ssz = bsz = 0;
for(int i = 1; i <= n; i++) vis[i] = 0;
for(int i = 1; i <= n; i++) {
if(!vis[i]) DFS(i, 0);
}
for(int i = 1; i <= n; i++) vis[i] = 0;
for(int i = ssz; i >= 1; i--) {
if(!vis[Stack[i]]) DFS(Stack[i], ++bsz);
}
}

int n, m;
int A[10005], B[10005], C[10005];
bool check(int x) {
edge_init();
for(int i = 1; i <= x; i++) {
int u = A[i], v = B[i]; u++; v++;
if(C[i] == 0) {
edge_add(u + n, v); edge_add(v + n, u);
}
if(C[i] == 1) {
edge_add(u + n, v + n); edge_add(u, v);
edge_add(v + n, u + n); edge_add(v, u);
}
if(C[i] == 2) {
edge_add(u, v + n); edge_add(v, u + n);
}
}
tarjan(2 * n);
for(int i = 1; i <= n; i++) {
if(Belong[i] == Belong[i + n]) return false;
}
return true;
}
int solve() {
int l = 1, r = ::m, m;
while(l <= r) {
m = (l + r) >> 1;
if(check(m)) l = m + 1;
else r = m - 1;
}
return l - 1;
}
int main() {
int T; //FIN;
scanf("%d", &T);
while(T--) {
scanf("%d%d", &n, &m);
for(int i = 1; i <= m; i++) {
scanf("%d%d%d", &A[i], &B[i], &C[i]);
}
printf("%d\n", solve());
}
return 0;
}