Codechef REBXOR

#include<bits/stdc++.h>

using namespace std;

#define M 29
#define MAXN 400000+5
#define INF (int)1e9

int N;
int a[MAXN];
int L[MAXN];
int R[MAXN];

int id = 0;
struct node {
    int link[2];
    node() {
        link[0] = link[1] = -1;
    }
};
node trie[30 * MAXN];

int new_node() {
    return id++;
}

inline void insert(int cur, int v) {
    int two_p = (1<<M);
    for (int i = 0; i <= M; i++) {
        int nxt = (v & two_p) != 0;
        if (trie[cur].link[nxt] == -1)  trie[cur].link[nxt] = new_node();
        cur = trie[cur].link[nxt];
        two_p >>= 1;
    }
}

inline int find_max(int cur, int v) {
    int ans = 0, two_p = (1<<M);
    for (int i = 0; i <= M; i++) {
        int nxt = (v & two_p) != 0;
        if (trie[cur].link[1 - nxt] != -1) {
            ans ^= two_p;
            cur = trie[cur].link[1 - nxt];
        } else {
            cur = trie[cur].link[nxt];
        }
        two_p >>= 1;
    }
    return ans;
}

void clear_trie() {
    for (int i = 0; i <= id; i++) {
        trie[i].link[0] = -1;
        trie[i].link[1] = -1;
    }
    id = 0;
}

int root_L;
int root_R;

int main() {
    scanf("%d", &N);
    int ans = 0;

    int lval = 0;
    root_L = new_node();
    insert(root_L, 0);
    for (int i = 0; i < N; i++) {
        scanf("%d", &a[i]);
        lval ^= a[i];
        L[i] = max((i == 0) ? 0 : L[i-1], find_max(root_L, lval));
        insert(root_L, lval);
    }

    clear_trie();
    int rval = 0;
    root_R = new_node();
    insert(root_R, 0);
    for (int i = N-1; i > 0; i--) {
        rval ^= a[i];
        R[i] = max((i == N-1) ? 0 : R[i+1], find_max(root_R, rval));
        insert(root_R, rval);
        int cand = R[i] + (i == 0 ? -INF : L[i-1]);
        if (cand > ans) ans = cand;
    }
    printf("%d\n", ans);
}