79 lines
2.6 KiB
C
79 lines
2.6 KiB
C
// 优化版：每个区间长度 k(1..n) 的最大区间价值 max(subarray_max * subarray_min)
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// 算法：最大值笛卡尔树 + 跨越合并（单调两指针），整体显著优于 O(n^2)
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// 说明：对每个树节点 i 及其覆盖段 [l,r]，所有包含 i 的子数组最大值均为 a[i]；
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// 设从 i 向左取 x 个、向右取 y 个，长度 k=x+y+1，区间最小值为 min(Lmin[x], Rmin[y])；
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// 其中 Lmin/Rmin 为以 i 为中心的左/右最小值前后缀。对固定 s=x+y，
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// 利用两指针在可行范围内最大化 min(Lmin[s-y], Rmin[y])，O(lenL+lenR) 完成一次合并。
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#include <stdio.h>
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#include <stdlib.h>
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typedef long long ll;
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static inline ll minll(ll a, ll b) { return a < b ? a : b; }
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// 构建“以最大值为堆”的笛卡尔树。相等值用 <= 弹出以保证唯一性（倾向右侧作为父）。
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// 输出：left child lc，right child rc，parent；返回根下标。
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static int build_cartesian_tree(const ll *a, int n, int *lc, int *rc, int *parent) {
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int *st = (int*)malloc((n + 1) * sizeof(int));
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int top = 0;
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int root = 0;
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for (int i = 1; i <= n; ++i) {
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int last = 0;
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while (top > 0 && a[st[top - 1]] <= a[i]) {
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last = st[--top];
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}
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if (top > 0) {
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rc[st[top - 1]] = i;
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parent[i] = st[top - 1];
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} else {
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root = i;
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parent[i] = 0;
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}
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lc[i] = last;
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if (last) parent[last] = i;
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st[top++] = i;
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}
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free(st);
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return root;
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}
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int main(void) {
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int n;
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if (scanf("%d", &n) != 1) return 0;
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int cap = n + 5;
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int *dq = (int*)malloc((size_t)cap * sizeof(int));
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int head = 0, tail = 0, size = 0;
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char *out = (char*)malloc((size_t)(n * 14 + 1));
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int pos = 0;
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for (int i = 0; i < n; ++i) {
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int op;
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scanf("%d", &op);
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if (op == 1) {
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int x; scanf("%d", &x);
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head = (head - 1 + cap) % cap;
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dq[head] = x;
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++size;
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} else if (op == 2) {
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int x; scanf("%d", &x);
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dq[tail] = x;
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tail = (tail + 1) % cap;
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++size;
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} else if (op == 3) {
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pos += sprintf(out + pos, "%d\n", dq[head]);
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} else if (op == 4) {
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int idx = (tail - 1 + cap) % cap;
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pos += sprintf(out + pos, "%d\n", dq[idx]);
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} else if (op == 5) {
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head = (head + 1) % cap;
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--size;
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} else if (op == 6) {
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tail = (tail - 1 + cap) % cap;
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--size;
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}
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}
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fwrite(out, 1, (size_t)pos, stdout);
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free(out);
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free(dq);
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return 0;
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} |