func_code_string: #include <bits/stdc++.h>   using namespace std;   const int INF = 1e9, MOD = 1e9 + 7, N = 1e5 + 1, M = 20;   void setIO(string name =   ) {     ios::sync_with_stdio(false);     cin.tie(0);     if (name.size()) {       freopen((name +  .in ).c_str(),  r , stdin);       freopen((name +  .out ).c_str(),  w , stdout);     }   }   int n, m, a[N], s, pxor[1000001], ans[N];   void pre() {     pxor[0] = 0;     for (int i = 1; i < 1000001; i++) pxor[i] = pxor[i - 1] ^ i;   }   string bit(int j) {     string ans;     for (int i = 0; i < M; i++) {       ans += (j & 1) +  0 ;       j >>= 1;     }     reverse(ans.begin(), ans.end());     return ans;   }   struct node1 {     int mx = -INF;     node1 *nxt[2]{};   };   struct node2 {     int mn = INF;     node2 *nxt[2]{};   };   node1 *rt1 = new node1();   node2 *rt2 = new node2();   void insert1(node1 *o, int i) {     string s = bit(pxor[i]);     for (char c : s) {       if (!o->nxt[c -  0 ]) o->nxt[c -  0 ] = new node1();       o = o->nxt[c -  0 ];       o->mx = max(o->mx, i);     }   }   void insert2(node2 *o, int i) {     string s = bit(pxor[i]);     for (char c : s) {       if (!o->nxt[c -  0 ]) o->nxt[c -  0 ] = new node2();       o = o->nxt[c -  0 ];       o->mn = min(o->mn, i);     }   }   void insert(int i) {     insert1(rt1, i);     insert2(rt2, i - 1);   }   int get1(node1 *o, int i) {     string s = bit(pxor[i]);     int ans = 0, shift = M - 1;     for (char c : s) {       int tmp = 1 ^ (c -  0 );       if (o->nxt[tmp] && o->nxt[tmp]->mx > i) {         o = o->nxt[tmp];         ans += (1 << shift);       } else if (o->nxt[1 ^ tmp] && o->nxt[1 ^ tmp]->mx > i) {         o = o->nxt[tmp ^ 1];       } else         return 0;       shift--;     }     return ans;   }   int get2(node2 *o, int i) {     string s = bit(pxor[i]);     int ans = 0, shift = M - 1;     for (char c : s) {       int tmp = 1 ^ (c -  0 );       if (o->nxt[tmp] && o->nxt[tmp]->mn < i) {         o = o->nxt[tmp];         ans += (1 << shift);       } else if (o->nxt[1 ^ tmp] && o->nxt[1 ^ tmp]->mn < i) {         o = o->nxt[tmp ^ 1];       } else         return 0;       shift--;     }     return ans;   }   int get(int i) { return max(get1(rt1, i - 1), get2(rt2, i)); }   void clearall(node1 *o) {     o->mx = -INF;     if (o->nxt[0] && o->nxt[0]->mx != -INF) clearall(o->nxt[0]);     if (o->nxt[1] && o->nxt[1]->mx != -INF) clearall(o->nxt[1]);   }   void clearall(node2 *o) {     o->mn = INF;     if (o->nxt[0] && o->nxt[0]->mn != INF) clearall(o->nxt[0]);     if (o->nxt[1] && o->nxt[1]->mn != INF) clearall(o->nxt[1]);   }   void init() {     clearall(rt1);     clearall(rt2);   }   struct query {     int l, r, id, bl;     query(int ll, int rr, int i) : l(ll), r(rr), id(i), bl(l / s) {}     bool operator<(const query &other) const {       return make_pair(bl, r) < make_pair(other.bl, other.r);     }   };   query make_query(int ll, int rr, int i) { return query(ll, rr, i); }   vector<query> qry;   signed main() {     setIO();     pre();     cin >> n >> m;     s = ceil(sqrt(n));     for (int i = 0; i < n; i++) cin >> a[i];     for (int i = 0; i < m; i++) {       int l, r;       cin >> l >> r;       qry.push_back(make_query(l - 1, r - 1, i));     }     sort(qry.begin(), qry.end());     for (int i = 0, j = 0; i < m; i = j) {       while (j < m && qry[j].bl == qry[i].bl) j++;       int lmx = 0, mid = j, right, nowmx = 0;       for (int k = i; k < j; k++) right = lmx = max(lmx, qry[k].l);       for (int k = i; k < j; k++)         if (qry[k].r > lmx) {           mid = k;           break;         }       init();       for (int k = mid; k < j; k++) {         ans[qry[k].id] = nowmx;         while (right <= qry[k].r) {           insert(a[right]);           nowmx = ans[qry[k].id] = max(ans[qry[k].id], get(a[right]));           right++;         }         for (int l = lmx; l >= qry[k].l; l--) {           ans[qry[k].id] = max(ans[qry[k].id], get(a[l]));         }       }       for (int k = i; k < j; k++) {         init();         for (int l = min(qry[k].r, lmx); l >= qry[k].l; l--) {           insert(a[l]);           ans[qry[k].id] = max(ans[qry[k].id], get(a[l]));         }       }     }     for (int i = 0; i < m; i++) cout << ans[i] <<   n ;   }   