技巧(二)

O(n^2) -> O(n) -> O(1);

排除奇数, n/2. 要0,  n/2+1; 枚举x, y; 

#include <cstdio>
int main()
{
    long long n; int t, Q=1; scanf("%d", &t);
    while(t--)
    { 
        long long cnt=0;
        scanf("%lld", &n);
        /*for(int i=0; i<=n; i++)
        {
            if((n-i) & 1)
                continue;
            int Q=(n-i)/2; 
            if(Q==0)
            {
                cnt+=1;
            }
            else
            {
                 cnt=cnt+(1+Q)*Q/2;
                cnt+=1;
            }
        }*/
        n=n/2+1;
        cnt=(n+1)*n/2;
        printf("Case #%d: %lld\n", Q++, cnt);
    }
    return 0;
}

 

转载于:https://www.cnblogs.com/soTired/p/5374597.html