HDU4258+DP+斜率优化

对于斜率优化的dp还不是很懂。。。。。。。。。

/*
dp+斜率优化
*/
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<algorithm>
#include<iostream>
#include<queue>
#include<math.h>
using namespace std;
const int maxn = 1000005;
const int cl = 0x7F;
typedef __int64 int64;
int64 a[ maxn ],dp[ maxn ];
int que[ maxn ];
double get( int64 x,int64 y ){
    return 1.0*( dp[x]-dp[y]+a[x+1]*a[x+1]-a[y+1]*a[y+1] )/( 2.0*(a[x+1]-a[y+1]) );
}
void dp_solve( int64 n,int64 c ){
    memset( dp,cl,sizeof( dp ) );
    dp[ 0 ] = 0;
    int head,tail;
    head = tail = 1;
    que[ 1 ] = 0;
    for( int i=1;i<=n;i++ ){
         while( head<tail&&get( que[ head+1 ],que[ head ] )<=(double)a[ i ]  )
             head++;
         dp[ i ] = dp[ que[head] ]+c+( a[i]-a[ que[head]+1 ])*( a[i]-a[ que[head]+1 ] );
         while( head<tail&&get( i,que[ tail ] )<=get( que[ tail ],que[ tail-1 ] ) )
             tail--;
         que[ ++tail ] = i;
    }
    printf("%I64d\n",dp[ n ]);
    return ;
}
int main(){
    int64 n,c;
    while( scanf("%I64d%I64d",&n,&c)==2 ){
        if( n==0 && c==0 ) break;
        for( int i=1;i<=n;i++ )
            scanf("%I64d",&a[ i ]);
        dp_solve( n,c );
    }
    return 0;
}