Hdu--4991（树状数组，离散化，DP）
2014-09-09 14:05:21
思路：用树状数组来优化DP过程，详情见Bestcoder题解，本来用以前学过的离散化来写。。结果搞不定，于是重新学了个离散化：推荐博客
离散化思路：用b[]数组用来做a[]数组的副本，然后就是unique，以及lower_bound函数的调用了。
1 /************************************************************************* 2 > File Name: hdu4991.cpp 3 > Author: Nature 4 > Mail: 564374850@qq.com 5 > Created Time: Mon 08 Sep 2014 10:47:42 PM CST 6 ************************************************************************/ 7 8 #include <cstdio> 9 #include <cstring> 10 #include <cstdlib> 11 #include <cmath> 12 #include <vector> 13 #include <queue> 14 #include <iostream> 15 #include <algorithm> 16 using namespace std; 17 typedef long long ll; 18 const int INF = 1 << 29; 19 const int maxn = 10010; 20 const ll mod = 123456789; 21 22 int a[maxn],b[maxn],n,m; 23 ll c[105][maxn]; 24 25 int Lowbit(int x){ 26 return x & (-x); 27 } 28 void Update(int x,int d,int k){ 29 while(x <= maxn){ 30 c[k][x] = (c[k][x] + d) % mod; 31 x += Lowbit(x); 32 } 33 } 34 ll Getsum(int x,int k){ 35 ll res = 0; 36 while(x){ 37 res = (res + c[k][x]) % mod; 38 x -= Lowbit(x); 39 } 40 return res; 41 } 42 43 int main(){ 44 while(scanf("%d%d",&n,&m) != EOF){ 45 memset(c,0,sizeof(c)); 46 for(int i = 1; i <= n; ++i){ 47 scanf("%d",a + i); 48 b[i] = a[i]; 49 } 50 sort(b + 1,b + n + 1); 51 int size = unique(b + 1,b + n + 1) - b - 1; 52 for(int i = 1; i <= n; ++i) 53 a[i] = lower_bound(b + 1,b + size + 1,a[i]) - b; 54 ll tmp; 55 for(int i = 1; i <= n; ++i){ 56 Update(a[i],1,1); 57 for(int j = 1; j < m; ++j){ 58 tmp = Getsum(a[i] - 1,j); 59 if(!tmp) break; 60 Update(a[i],tmp,j + 1); 61 } 62 } 63 printf("%lld\n",Getsum(maxn,m) % mod); 64 } 65 return 0; 66 }
