POJ 1701

 /*
 Every tenant went up N floors would make the dissatisfied degree rise N * a + 0.5 * N * (N - 1) degrees,
 every tenant went down N floors would make the dissatisfied degree rise N * b + 0.5 * N * (N - 1) degrees. 

   △= Dp+1 – Dp
 = ∑1=<i<=p Ki*(b+p-i)) - ∑p<i<=n Ki*(a+i-p-1)
 =  ∑1=<i<=n Ki * i +(b+p)*∑1=<i<=p Ki   -     (a-p-1)∑p<i<=n Ki
 */

 #include <iostream>
 #define MAXN  10001
 using namespace std;

 __int64 _m[MAXN+];
 int k[MAXN+];
 __int64 p_2[MAXN+];
 __int64 p_3[MAXN+];
 int k_1[MAXN];
 int k_2[MAXN];

 int main()
 {
     //freopen("acm.acm","r",stdin);
     int test;
     int n;
     int i;
     int j;
     int  p_1;
     int a;
     int b;
     scanf("%d",&test);
     while(test --)
     {
         scanf("%d",&n);
         scanf("%d",&a);
         scanf("%d",&b);

         for(i = ; i <= n; ++ i)
         {
             scanf("%d",&k[i]);
         }

         for(i = ; i <= n; ++ i)
         {
             k_1[i] = k_2[i] = k[i];
         }

         for(i = n-; i >=; -- i)
         {
             k_2[i] += k_2[i+];
         }

         for(i = ; i <= n; ++i)
         {
             k_1[i] += k_1[i-];
         }

         p_1 = ;
         for(i = ; i <= n; ++ i)
         {
             p_1 += k[i]*i;
         }

         for(i = ; i <= n; ++ i)
         {
             p_2[i] = (b + i)*k_1[i];
         }

         for(i = ; i <= n; ++ i)
         {
             k_2[i] -= k[i];
         }

         copy(k_2,k_2+n+,p_3);

         for(i = ; i <= n; ++ i)
         {
             p_3[i] *= (a-i-);
         }
         _m[] = ;
         for(i = ; i <= n; ++ i)
         {
             _m[] += (i-)*a+((i-)*(i-)/);
         }

         for(i = ; i <= n; ++ i)
         {
             _m[i] = _m[i-] - p_1 + p_2[i-] - p_3[i-];
         }

         __int64 min = ;

         int place;

         for(i = ; i <= n; ++ i)
         {
             if(_m[i] < min)
             {
                 min = _m[i];
                 place = i;
             }
         }
         cout<<place<<endl;
     }
 }

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