Bzoj 4260:codechef Rebxor (trie)

With the prefix and, the maximum XOR value ending with the X element is max (sum_{x^sumP) (1≤P<X), which is accelerated with trie. Suffix the same, and then sweep it again OK. Time Complexity O ( 31N)}

-----------------------------------------------------------------------

#include <cstdio>#include <cstring>#include <algorithm>#include <cctype>using namespace std; const int MAXN = 400009;const int n = +;int Read () {char C = getchar (); int ret = 0;For (;!isdigit (c); c = GetChar ());For (; IsDigit (c); c = GetChar ()) ret = RET * + C-' 0 ';return ret;}int SEQ[MAXN], L[MAXN], R[MAXN];int N;struct Node {node* ch[2];} POOL[MAXN * n], *pt, *root;void init () {memset (pool, 0, sizeof pool);pt = pool; root = pt++;} 

void Insert (int x) {

node* t = root;for (int i = n; i--;) {int v = (x >> i) & 1;if (!t->ch[v]) t->ch[v] = pt++;t = t->ch[v];}}int Find (int x) {node* t = root;int ret = 0;for (int i = n; i--;) {int v = ((((x >> i) & 1) ^ 1);if (T->ch[v])ret |= 1 << i, t = t->ch[v];Elset = t->ch[v ^ 1];}return ret;}int main () {N = read ();for (int i = 1; I <= N; i++) Seq[i] = read ();int sum = l[0] = 0;init (); Insert (sum);for (int i = 1; I <= N; i++) {sum ^= seq[i];L[i] = max (l[i-1], Find (sum));Insert (sum);}sum = r[n + 1];init (); Insert (sum);for (int i = N; i; i--) {sum ^= seq[i];R[i] = max (r[i + 1], Find (sum));Insert (sum);}int ans = 0;for (int i = 1; i < N; i++)ans = max (ans, l[i] + r[i + 1]);printf ("%d\n", ans);return 0;}

-----------------------------------------------------------------------

4260:codechef rebxor Time limit: Sec Memory Limit: + MB
Submit: Solved: 76
[Submit] [Status] [Discuss] Description

The first line of input data contains an integer n representing the number of elements in the array. The second line contains n integers a1,a2,..., an.

The output line contains the maximum possible value for the given expression.

Sample Input5
1 2 3) 1 2Sample Output6HINT

The conditions are met (L1,R1,L2,R2): (1,2,3,3), (1,2,4,5), (3,3,4,5).
For 100% of data, 2≤n≤4*105,0≤ai≤109.

Source

by yts1999

Bzoj 4260:codechef Rebxor (trie)