原题 - 【FJOI2016】神秘数
如果只有一次全局询问,可以排序之后扫一遍数组,每次和比较,更新答案,直到不能更新为止
区间询问不能排序,但是如果不排序的话,进行上述操作,最多扫次就能得出答案
考虑每次更新时,可以更新的数一定比上一次更新时的大(否则在上一次更新就计入里了),于是我们最多会更新次
于是我们就有了一个主席树的做法去优化找小于某个值的做法,复杂度
#include <iostream> #include <cstdio> #include <cmath> #include <cstring> #include <algorithm> #include <queue> #define ub(x) (upper_bound(b + 1, b + n + 1, x) - b - 1) using namespace std; const int N = 8e7 + 10, M = 2e6 + 10, inf = 0x3f3f3f3f; inline int read() { bool sym = 0; int res = 0; char ch = getchar(); while (!isdigit(ch)) sym |= (ch == '-'), ch = getchar(); while (isdigit(ch)) res = (res << 3) + (res << 1) + (ch ^ 48), ch = getchar(); return sym ? -res : res; } int n, m, cnt, a[N], b[N], ls[N], rs[N], rt[N]; long long sum[N]; void insert(int &x, int y, int l, int r, int t) { x = ++cnt; ls[x] = ls[y]; rs[x] = rs[y]; sum[x] = sum[y] + b[t]; if (l == r) return; int mid = l + r >> 1; if (mid >= t) insert(ls[x], ls[y], l, mid, t); else insert(rs[x], rs[y], mid + 1, r, t); } long long query(int x, int y, int l, int r, int ln, int rn) { if (l > r) return 0; if (ln <= l && r <= rn) return sum[y] - sum[x]; int mid = l + r >> 1; if (mid >= rn) return query(ls[x], ls[y], l, mid, ln, rn); if (mid + 1 <= ln) return query(rs[x], rs[y], mid + 1, r, ln, rn); return query(ls[x], ls[y], l, mid, ln, rn) + query(rs[x], rs[y], mid + 1, r, ln, rn); } int main() { n = read(); m = read(); for (int i = 1; i <= n; i++) a[i] = read(), b[i] = a[i]; sort(b + 1, b + n + 1); int t = unique(b + 1, b + n + 1) - b - 1; for (int i = 1; i <= n; i++) { a[i] = lower_bound(b + 1, b + t + 1, a[i]) - b; insert(rt[i], rt[i - 1], 0, t, a[i]); } n = t; for (int i = 1; i <= m; i++) { int l = read(), r = read(); long long ans = 0, t = query(rt[l - 1], rt[r], 0, n, 0, ub(ans + 1)); while (t > ans) ans = t, t = query(rt[l - 1], rt[r], 0, n, 0, ub(ans + 1)); printf("%lld\n", ans + 1); } return 0; }