845--1777F - Comfortably Numb

1777F - Comfortably Numb

思路

单调栈预处理区间，然后对短的一边进行枚举，对长度一边匹配。

代码

#include <bits/stdc++.h>
using namespace std;
const int M = 2e5 + 5;

void Up_Stk(int n, int a[], int l[], int r[]) {
    for(int i = 1; i <= n; i++) {
        int j = i;
        while(j > 1 && a[j - 1] <= a[i])j = l[j -1];
        l[i] = j;
    }
    for(int i = n; i; i--) {
        int j = i;
        while(j < n && a[j + 1] < a[i])j = r[j + 1];
        r[i] = j;
    }
}

struct Lasting_01tire {
    const int N = 30;
    struct node {
        int ch[2], cnt;
    }tr[M * 32];
    int rot[M], tot;
    void insert(int pre, int &now, int i, int x) {
        tr[now = ++tot] = tr[pre];
        tr[now].cnt++;
        if(i < 0)return ;
        int v = x >> i & 1;
        tr[now].ch[v ^ 1] = tr[pre].ch[v ^ 1];
        insert(tr[pre].ch[v], tr[now].ch[v], i - 1, x);
    }
    int query(int l, int r, int x) {//直接传入你需要匹配的范围就可以了
        l = l > 1 ? rot[l - 2] : 0;
        r = rot[r];
        int ans = 0;
        for(int i = N; i >= 0; i--) {
            int v = x >> i & 1;
            if(tr[tr[r].ch[v ^ 1]].cnt - tr[tr[l].ch[v ^ 1]].cnt) {
                ans += 1 << i;
                l = tr[l].ch[v ^ 1];
                r = tr[r].ch[v ^ 1];
            }
            else {
                l = tr[l].ch[v];
                r = tr[r].ch[v];
            }
        }
        return ans;
    }
    void reset(int n) {
        for(int i = 0; i <= n + 1; i++)rot[i] = 0;
        for(int i = 0; i <= tot; i++)
            tr[i].ch[0] = tr[i].ch[1] = tr[i].cnt = 0;
        tot = 0;
    }
    void build(int n, int sum[]) {//这里是已经前缀和过的数组
        reset(n);
        insert(0, rot[0], N, 0);
        for(int i = 1; i <= n; i++)
            insert(rot[i - 1], rot[i], N, sum[i]);
    }
}Tr;

int a[M], sum[M], l[M], r[M];
int f(int now, int l, int r) {
    int ans = 0;
    if(r - now > now - l) {//固定左边，匹配右边
        for(int i = l; i <= now; i++)
            ans = max(ans, Tr.query(now + 1, r, sum[i - 1] ^ a[now]));
    }
    else {//固定右边，匹配左边
        for(int i = now; i <= r; i++)
            ans = max(ans, Tr.query(l, now - 1, sum[i] ^ a[now]));
    }
    return ans;
}

void solve() {
    int n; cin >> n;
    for(int i = 1; i <= n; i++) {
        cin >> a[i];
        sum[i] = sum[i - 1] ^ a[i];
    }
    Up_Stk(n, a, l, r);
    Tr.build(n, sum);
    int ans = 0;
    for(int i = 1; i <= n; i++)
        ans = max(ans, f(i, l[i], r[i]));
    cout << ans << '\n';
}

int main() {
    ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    int TT; cin >> TT;
    while(TT--) {
        solve();
    }
    return 0;
}