Bzoj1046 [haoi2007] ascending sequence

Ah, noip difficulty question... I spent half a day in the workshop...

Well, first we need to find the LIS length.

Then we are greedy. Suppose we have found the X item of the answer, and then find the x + 1 item backward:

We found that you only need to find the first a [I] that meets f [I]> = l-x.

 1 /************************************************************** 2     Problem: 1046 3     User: rausen 4     Language: C++ 5     Result: Accepted 6     Time:1772 ms 7     Memory:960 kb 8 ****************************************************************/ 9  10 #include <cstdio>11 #include <algorithm>12  13 using namespace std;14 const int N = 10005;15 const int inf = (int) 1e9;16 int f[N], a[N], b[N];17 int len, n;18 int ans[N];19  20 inline int read(){21     int x = 0, sgn = 1;22     char ch = getchar();23     while (ch < ‘0‘ || ch > ‘9‘){24         if (ch == ‘-‘) sgn = -1;25         ch = getchar();26     }27     while (ch >= ‘0‘ && ch <= ‘9‘){28         x = x * 10 + ch - ‘0‘;29         ch = getchar();30     }31     return sgn * x;32 }33  34 void pre_work(){35     len = 1;36     int l, r, mid;37     for (int i = 2; i <= n; ++i)38         b[i] = -inf;39     b[0]= inf, b[1] = a[1], f[1] = 1;40     for (int i = 2; i <= n; ++i){41         l = 0, r = len + 1;42         while (l + 1 < r){43             mid = (l + r) >> 1;44             if (b[mid] > a[i]) l = mid;45             else r = mid;46         }47         len = max(len, ++l);48         b[l] = max(b[l], a[i]);49         f[i] = l;50     }51     reverse(a + 1, a + n + 1);52     reverse(f + 1, f + n + 1);53 }54  55 void work(int l){56     if (len < l){57         printf("Impossible\n");58         return;59     }60     int cnt = 0, last = -inf;61     for (int i = 1; i <= n && l != 0; ++i)62         if (f[i] >= l && a[i] > last)63             ans[++cnt] = i, --l, last = a[i];64     for (int i = 1; i < cnt; ++i)65         printf("%d ", a[ans[i]]);66     printf("%d\n", a[ans[cnt]]);67 }68  69 int main(){70     n = read();71     for (int i = n; i; --i)72         a[i] = read();73     pre_work();74     int m = read(), X;75     while (m--){76         X = read();77         work(X);78     }79     return 0;80 }

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Bzoj1046 [haoi2007] ascending sequence