poj 3764 The xor-longest Path Trie

题目链接

求树上的一条最长异或路径。

定义f(u, v)为u到v的路径， 那么显然f(1, u)^f(1, v) = f(u, v)， 想不到这个就没有办法做。

然后就可以用字典树查询+插入了。

用指针版本的狂T不止。

#include <iostream>
#include <vector>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <map>
#include <set>
#include <string>
#include <queue>
#include <stack>
#include <bitset>
using namespace std;
#define pb(x) push_back(x)
#define ll long long
#define mk(x, y) make_pair(x, y)
#define lson l, m, rt<<1
#define mem(a) memset(a, 0, sizeof(a))
#define rson m+1, r, rt<<1|1
#define mem1(a) memset(a, -1, sizeof(a))
#define mem2(a) memset(a, 0x3f, sizeof(a))
#define rep(i, n, a) for(int i = a; i<n; i++)
#define fi first
#define se second
typedef pair<int, int> pll;
const double PI = acos(-1.0);
const double eps = 1e-8;
const int mod = 1e9+7;
const int inf = 1061109567;
const int dir[][2] = { {-1, 0}, {1, 0}, {0, -1}, {0, 1} };
const int maxn = 2e5+5;
int head[maxn*2], num, val[maxn], top = 31, cnt;
struct node
{
    int to, nextt, w;
}e[maxn*2];
void add(int u, int v, int w) {
    e[num].to = v, e[num].w = w, e[num].nextt = head[u], head[u] = num++;
}
void init() {
    num = cnt = 0;
    mem(val);
    mem1(head);
}
void dfs(int u, int fa) {
    for(int i = head[u]; ~i; i = e[i].nextt) {
        int v = e[i].to;
        if(v == fa)
            continue;
        val[v] = val[u]^e[i].w;
        dfs(v, u);
    }
}
struct Trie
{
    int next[2];
    void init() {
        next[0] = next[1] = 0;
    }
}trie[maxn];
void insert(int pre) {
    int p = 0;
    for(int i = top-1; i>=0; i--) {
        int tmp = pre>>i&1;
        if(!trie[p].next[tmp]) {
            trie[p].next[tmp] = ++cnt;
            trie[cnt].init();
        }
        p = trie[p].next[tmp];
    }
}
int query(int pre) {
    int p = 0, ret = 0;
    for(int i = top-1; i>=0; i--) {
        int tmp = pre>>i&1;
        if(trie[p].next[tmp^1]) {
            ret |= 1<<i;
            tmp ^= 1;
        }
        p = trie[p].next[tmp];
    }
    return ret;
}
int main()
{
    int n, x, y, z;
    while(~scanf("%d", &n)) {
        init();
        for(int i = 0; i<n-1; i++) {
            scanf("%d%d%d", &x, &y, &z);
            add(x, y, z);
            add(y, x, z);
        }
        val[0] = 0;
        dfs(0, -1);
        int ans = 0;
        trie[0].init();
        for(int i = 0; i<n; i++) {
            insert(val[i]);
            ans = max(ans, query(val[i]));
        }
        printf("%d
", ans);
    }
    return 0;
}