C++博客-Life is Good.-随笔分类-C/C++面试题目

10亿个浮点数,求出其中最大的10000个.

Mike Song — Thu, 02 Jun 2011 08:51:00 GMT

#include "stdafx.h"
#include <vector>
#include <iostream>
#include <algorithm>
#include <functional> // for greater<>
using namespace std;

int _tmain(int argc, _TCHAR* argv[])
{
  vector<float> bigs(10000,0);
  vector<float>::iterator it;

  // Init vector data
  for (it = bigs.begin(); it != bigs.end(); it++)
  {
    *it = (float)rand()/7; // random values;
  }

  cout << bigs.size() << endl;

  make_heap(bigs.begin(),bigs.end(), greater<float>()); // The first one is the smallest one!

  float ff;
  for (int i = 0; i < 1000000000; i++)
  {
    ff = (float) rand() / 7;
    if (ff > bigs.front()) // replace the first one ?
    {
      // set the smallest one to the end!
      pop_heap(bigs.begin(), bigs.end(), greater<float>());

      // remove the last/smallest one
      bigs.pop_back();

      // add to the last one
      bigs.push_back(ff);

      // mask heap again, the first one is still the smallest one
      push_heap(bigs.begin(),bigs.end(),greater<float>());
    }
  }

  // sort by ascent
  sort_heap(bigs.begin(), bigs.end(), greater<float>());

  // sort by descent
  //sort_heap(bigs.begin(), bigs.end());
  //sort_heap(bigs.begin(), bigs.end(), less());

  return 0;
}

Mike Song 2011-06-02 16:51 发表评论

字符串中的单词逆序排列

Mike Song — Wed, 01 Jun 2011 16:18:00 GMT

题目:
给定一个字符串, 该字符串由英文单词构成, 该函数的作用是把这个字符串中的单词逆序排列, 比如输入字符串为"This is a dog", 那么运行该函数后该字符串应转化为"dog a is This"

算法: 逆序所有字符串,然后再逆序所有单词, 两者顺序无所谓!

char* Reverse(char* start, char* end)
{
  if (start == NULL || *start == '\0' || end == NULL || *end == '\0')
    return NULL;

  char* p = start; // 首地址
  char ch;
  while(start < end)
  {
    ch = *start;
    *start++ = *end;
    *end-- = ch;
  }

  return p;
}

char* ReverseEveryWord(char* p)
{
  if (p == NULL || *p == '\0')
    return NULL;

  char* left= p;
  char* right = p;

  while(*right)
  {
    if (*right == ' ' || *right == '\0')
    {
      Reverse(left,right-1);
      left = right+1;
    }

    right++;
  }

  // Revere last word
  Reverse(left, right-1);

  return p;
}

char* ReverseWholeString(char* p)
{
  if (p == NULL || *p == '\0')
    return NULL;

  char* start = p;

  while(*p++)
    ;

  p -= 2; // 最后一个字符的地址

  return Reverse(start, p);
}

int _tmain(int argc, _TCHAR* argv[])
{
  char str[] = "This is a dog";
  ReverseWholeString(str);
  ReverseEveryWord(str);
  return 0;
}

Mike Song 2011-06-02 00:18 发表评论