codeforces-214(Div. 2)-C. Dima and Salad+DP恰好背包花费

//learnt and created at 2018/2/7
 #include <cstdio>
 #include <algorithm>
 #include <cstring>
 using namespace std;
 int n,k;
 int a[110],b[110];
 int dp[50020],mid = 25000;
 int main(){
    scanf("%d%d",&n,&k);
    for(int i=1; i<=n; i++)
    {
        scanf("%d",&a[i]);
    }
    for(int i=1; i<=n; i++)
    {
        scanf("%d",&b[i]);
        b[i] = a[i] - b[i]*k;
    }
    memset(dp,-1,sizeof(dp));　　　　　　　　//把dp数组初始化为-1；只把dp[25000]=0；
    dp[mid]=0;
    for(int i=1; i<=n; i++)
    {
        if(b[i]>=0)
        {
            for(int j=50000; j>=b[i]; j--)
            {
                if(dp[j-b[i]] !=-1)
                    dp[j] = max(dp[j-b[i]]+a[i],dp[j]);
            }
        }
        else
        {
            for(int j=0; j<=50000+b[i]; j++)
            {
                if(dp[j-b[i]]!=-1)
                    dp[j] =max(dp[j-b[i]]+a[i],dp[j]);
            }
        }
    }
    if(dp[mid]==0)puts("-1");
    else printf("%d\n",dp[mid]);

    return 0;
 }