洛谷 P3205 [HNOI2010]合唱隊
阿新 • • 發佈:2018-11-05
題目連結
題解
區間dp
\(f[i][j]\)表示i~j區間最後一次插入的是\(a[i]\)
\(g[i][j]\)表示i~j區間最後一次插入的是\(a[j]\)
然後就是普通區間dp轉移
Code
#include<bits/stdc++.h> #define LL long long #define RG register inline int gi() { bool f = 0; char c = getchar(); RG int x = 0; while (c!='-' && (c < '0' || c > '9')) c = getchar(); if (c == '-') f = 1, c = getchar(); while (c >= '0' && c <= '9') x = x*10+c-'0', c = getchar(); return f ? -x:x; } using namespace std; const int N = 1010, Mod = 19650827; int a[N], f[N][N], g[N][N]; //f最後一次插在前面,g插在後面 int main() { int n = gi(); for (int i = 1; i <= n; i++) a[i] = gi(); for (int i = 1; i <= n; i++) f[i][i] = 1; for (int len = 1; len < n; len++) { for (int i = 1; i+len <= n; i++) { int j = i+len; f[i][j] = (f[i+1][j]*(a[i+1]>a[i]) + g[i+1][j]*(a[j]>a[i])) % Mod; g[i][j] = (g[i][j-1]*(a[j]>a[j-1]) + f[i][j-1]*(a[i]<a[j])) % Mod; } } printf("%d\n", (f[1][n]+g[1][n])%Mod); return 0; }