#1543. 【2022 正睿 NOIP 十连测 Day4】零二（Zero Two）

https://sjzezoj.com/submission/70995

S2OJ/1543/1543.cpp

@@ -0,0 +1,64 @@
+#include <iostream>
+#include <algorithm>
+#include <cstring>
+#include <iterator>
+#include <utility>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 105;
+const int mod = 998244353;
+
+int n, a[N], p[N], f[N][N][N];
+std::vector<std::pair<int, int>> nums;
+
+int solve(int l, int r, int x) {
+    if (x == 0) return 1;
+    if (l == r) return 1;
+    if (f[l][r][x] != -1) return f[l][r][x];
+
+    int pos = std::find(p + l, p + r + 1, x) - p;
+
+    if (pos > r) {
+        return f[l][r][x] = solve(l, r, x - 1);
+    }
+
+    int res = 0;
+
+    for (int i = pos; i <= r; i++) {
+        if (p[i] <= x) {
+            res = (res + static_cast<long long>(solve(l, i, x - 1)) * solve(i + 1, r, x) % mod) % mod;
+        }
+    }
+
+    return f[l][r][x] = res;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> a[i];
+
+        nums.emplace_back(a[i], i);
+    }
+
+    std::sort(nums.begin(), nums.end());
+    nums.erase(std::unique(nums.begin(), nums.end()), nums.end());
+
+    for (int i = 1; i <= n; i++) {
+        p[i] = std::distance(nums.begin(), std::lower_bound(nums.begin(), nums.end(), std::pair<int, int>{a[i], i}));
+    }
+
+    memset(f, 0xff, sizeof(f));
+
+    cout << solve(1, n, n) << endl;
+
+    return 0;
+}