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 + 10;  
const int inf = 0x3f3f3f3f;  
  
struct Edge {  
    ll val;  
    int v, nxt;  
} E[MAXN * 2];

int head[MAXN], id; 

void edge_init() {  
    id = 0;  
    memset(head, -1, 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[62], dis[MAXN];  

void Guass_base(void) {  
    memset(P, 0, sizeof(P));  
    for(int i = 1; i <= sz; i++) {  
        for(int j = 62; j >= 0; j--) {  
            if(!(A[i] >> j & 1)) continue;  
            if(!P[j]) {  
                P[j] = A[i]; break;  
            }  
            A[i] ^= P[j];  
        }  
    }  
}  

void DFS(int u, ll s) {  
    if(dis[u] == -1) 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 = 0;  
        edge_init();  
        memset(dis, -1, sizeof(dis));  
        for(int i = 1; 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(1, 0);  
        Guass_base();  
        ll ans = dis[n];  
        for(int i = 62; i >= 0; i--) {  
            ans = max(ans, ans ^ P[i]);  
        }  
        printf("%lld
", ans);  
    }  
    return 0;  
}