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  • Educational Codeforces Round 1 A. Tricky Sum 暴力

    A. Tricky Sum

    Time Limit: 20 Sec

    Memory Limit: 256 MB

    题目连接

    http://codeforces.com/contest/598/problem/A

    Description

    In this problem you are to calculate the sum of all integers from 1 to n, but you should take all powers of two with minus in the sum.

    For example, for n = 4 the sum is equal to  - 1 - 2 + 3 - 4 =  - 4, because 1, 2 and 4 are 20, 21 and 22 respectively.

    Calculate the answer for t values of n.

    Input

    The first line of the input contains a single integer t (1 ≤ t ≤ 100) — the number of values of n to be processed.

    Each of next t lines contains a single integer n (1 ≤ n ≤ 109).

    Output

    Print the requested sum for each of t integers n given in the input.

    Sample Input

    2
    4
    1000000000

    Sample Output

    -4
    499999998352516354

    HINT

    题意

    让你输出前n个数的和,但是如果遇到了2的次方,就是减去他

    题解:

    正常做法,就直接O(1)得到前n个数的和,然后再log判断前n个数的2的倍数的数是哪些就好了。

    但是我为什么脑抽了去写二分。。。

    代码

    #include<iostream>
    #include<vector>
    #include<stdio.h>
    #include<algorithm>
    using namespace std;
    
    vector<long long>Q;
    vector<long long>Sum;
    int main()
    {
        long long sum = 1;
        while(sum < 1e9+1)
        {
            Q.push_back(sum);
            sum*=2;
        }
        long long Sum1 = 0;
        for(int i=0;i<Q.size();i++)
        {
            Sum1 += Q[i];
            Sum.push_back(Sum1);
        }
        int t;scanf("%d",&t);
        while(t--)
        {
            long long n;cin>>n;
            long long ans = (1+n)*n/2;
            long long p = upper_bound(Q.begin(),Q.end(),n)-Q.begin();
            p--;
            ans -= 2*Sum[p];
            cout<<ans<<endl;
        }
    }
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  • 原文地址:https://www.cnblogs.com/qscqesze/p/4966136.html
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