HackerRank - "Manipulative Numbers"

最新推荐文章于 2025-08-07 17:23:55 发布

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最新推荐文章于 2025-08-07 17:23:55 发布

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原文链接：http://www.cnblogs.com/tonix/p/4565032.html

本文介绍了一种通过位运算找出数组中元素满足特定条件的关键位的方法。利用位运算的高效特性，该算法能够快速确定满足约束条件下存在的排列，并提供了一个具体的实现示例。

The answer by Tuxdude is perfect:

http://stackoverflow.com/questions/11161465/existence-of-a-permutation-under-constraints-interview-street-manipulative-nu

Lesson learnt: always try to dig more insightful thoughts to find hidden\subtle mechanisms.

#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <unordered_map>
using namespace std;


int main() 
{
    //    Get input
    int n; cin >> n;
    vector<int> in(n, 0);
    for(int i = 0; i < n; i ++)
        cin >> in[i];

    //
    int maxbit = floor(log(*std::max_element(in.begin(), in.end()))/log(2));
    int k = -1;
    for (int bitcnt = maxbit - 1; bitcnt >= 0; bitcnt --)
    {
        bool bValid = true;
        unordered_map<int, unsigned> rec;
        for(auto v : in)
        {
            int vs = v >> bitcnt;
            rec[vs] ++;
            if(rec[vs] > (n/2))
            {
                bValid = false;
                break;
            }
        }
        if(!bValid)
        {
            continue;
        }
        k = bitcnt;
        break;
    }
    cout << k << endl;
    return 0;
}