思路：
将数列合并之后使用线段树。边界条件容易写错。
实现：
1 #include <bits/stdc++.h> 2 using namespace std; 3 const int MAXN = 100005; 4 const int INF = 0x3f3f3f3f; 5 6 int a[MAXN], tree[MAXN * 4], n, m, sum[MAXN]; 7 vector<int> v(1, 0); 8 9 void build(int num, int l, int r) 10 { 11 if (l == r) { tree[num] = v[l]; return; } 12 int m = l + r >> 1; 13 build(num * 2, l, m); 14 build(num * 2 + 1, m + 1, r); 15 tree[num] = max(tree[num * 2], tree[num * 2 + 1]); 16 } 17 18 int query(int num, int l, int r, int x, int y) 19 { 20 if (x <= l && y >= r) return tree[num]; 21 int ans = -INF, m = l + r >> 1; 22 if (x <= m) ans = max(ans, query(num * 2, l, m, x, y)); 23 if (y >= m + 1) ans = max(ans, query(num * 2 + 1, m + 1, r, x, y)); 24 return ans; 25 } 26 27 int main() 28 { 29 scanf("%d %d", &n, &m); 30 for (int i = 0; i < n; i++) scanf("%d", &a[i]); 31 a[n] = INF; 32 int cnt = 2; 33 for (int i = 1; i < n; i++) 34 { 35 if (a[i] - a[i - 1] != a[i + 1] - a[i]) { v.push_back(cnt - 1); cnt = 2; } 36 else cnt++; 37 } 38 int tot = v.size() - 1; 39 build(1, 1, tot); 40 for (int i = 1; i <= tot; i++) sum[i] = sum[i - 1] + v[i]; 41 int l, r; 42 for (int i = 0; i < m; i++) 43 { 44 scanf("%d %d", &l, &r); 45 if (n == 1) { puts("1"); continue; } 46 int ls = lower_bound(sum + 1, sum + tot + 1, l == n ? l - 1 : l) - sum; 47 int rs = lower_bound(sum + 1, sum + tot + 1, r == n ? r - 1 : r) - sum; 48 int ans = -1; 49 if (ls == rs) ans = r - l + 1; 50 else 51 { 52 ans = max(sum[ls] - l + 2, r - sum[rs - 1]); 53 if (rs - ls > 1) ans = max(ans, query(1, 1, tot, ls + 1, rs - 1) + 1); 54 } 55 printf("%d ", ans); 56 } 57 return 0; 58 }