poj3670 eating together 简单的dp

   方法一：LIS/LDS#include"stdio.h" int lis[30001],lds[30001]; int main() { int n,t,len1=0,len2=0,i,left,right,mid; lds[0]=0x7fffffff; lis[0]=-1; scanf("%d",&n); for(i=1;i<=n;i++) { scanf("%d",&t); if(t>=lis[len1])lis[++len1]=t; else { left=0,right=len1-1; while(left<right) { mid=(left+right+1)>>1; if(lis[mid]<=t)left=mid; else right=mid-1; } lis[left+1]=t; } if(t<=lds[len2])lds[++len2]=t; else{ left=0,right=len2-1; while(left<right) { mid=(left+right+1)>>1; if(lds[mid]>=t)left=mid; else right=mid-1; } lds[left+1]=t; } } if(len1<len2)len1=len2; printf("%d\n",n-len1); return 0; }

方法2：看到某位大牛的代码很简洁，总结思路如下

以lis为例

设a为读取到的数，f[i][j]为前i个数且所有成员<=j时的最长lis长度，则有：

    f[i][1]=f[i-1]+(a==1);

   f[i][2]=max{f[i][1],f[i-1][2]}+(a==2);

   f[i][3]=max{f[i][2],f[i-1][3]}+(a==3);

 然后进行优化可得如下代码

 

#include"stdio.h" #include"stdlib.h" int max(int a,int b) {return a>b?a:b;} main() { int n,f[4]={0},g[4]={0},a,i; scanf("%d",&n); i=n; while(i--) { scanf("%d",&a); ++f[a],++g[a]; if(f[2]<f[1])f[2]=f[1]; if(f[3]<f[2])f[3]=f[2]; if(g[2]<g[3])g[2]=g[3]; if(g[1]<g[2])g[1]=g[2]; } printf("%d\n",n-max(f[3],g[1])); return 0; }