bzoj2115(线性基)

题目链接：http://www.lydsy.com/JudgeOnline/problem.php?id=2115

题意：求图中路径1~n上最大边权 xor 和

思路：参见 blog http://blog.csdn.net/qwb492859377/article/details/52939589

代码：

 #include <iostream>
 #include <stdio.h>
 #include <string.h>
 #define ll long long
 using namespace std;

 const int MAXN = 5e5 + ;
 const int inf = 0x3f3f3f3f;  

 struct Edge {
     ll val;
     int v, nxt;
 } E[MAXN * ];

 int head[MAXN], id; 

 void edge_init() {
     id = ;
     memset(head, -, sizeof(head));
 }  

 void edge_add(int u, int v, ll val) {
     E[id].v = v;
     E[id].val = val;
     E[id].nxt = head[u];
     head[u] = id++;
 }  

 int n, m, sz;
 ll A[MAXN], P[], dis[MAXN];  

 void Guass_base(void) {
     memset(P, , sizeof(P));
     for(int i = ; i <= sz; i++) {
         for(int j = ; j >= ; j--) {
             if(!(A[i] >> j & )) continue;
             if(!P[j]) {
                 P[j] = A[i]; break;
             }
             A[i] ^= P[j];
         }
     }
 }  

 void DFS(int u, ll s) {
     if(dis[u] == -) dis[u] = s;
     else {
         A[++sz] = s ^ dis[u];
         return;
     }
     for(int i = head[u]; ~i; i = E[i].nxt) {
         int v = E[i].v;
         DFS(v, s ^ E[i].val);
     }
 }  

 int main(void) {
     while(~scanf("%d%d", &n, &m)) {
         sz = ;
         edge_init();
         memset(dis, -, sizeof(dis));
         for(int i = ; i <= m; i++) {
             int u, v;
             ll val;
             scanf("%d%d%lld", &u, &v, &val);
             edge_add(u, v, val);
             edge_add(v, u, val);
         }
         DFS(, );
         Guass_base();
         ll ans = dis[n];
         for(int i = ; i >= ; i--) {
             ans = max(ans, ans ^ P[i]);
         }
         printf("%lld\n", ans);
     }
     return ;
 }