编程之美（数组求最大最小值得方法）

 #include <iostream>
    using namespace std;
    #include <assert.h>
    //分治思想求数组最大最小值
    void MaxandMin(int* a,int start,int end,int &Max,int &Min)
    {
      if(end-start<=1)
      {
         if(a[start] > a[end])
    {
      Max = a[start];
      Min = a[end];
    }
    else
    {
      Max = a[end];
      Min = a[start];
    }
    return;
      }
      int RightMax=0;
      int RightMin=0;
      int LeftMax=0;
      int LeftMin=0;
    MaxandMin(a,start,(start+end)/2,LeftMax,LeftMin);
    MaxandMin(a,(start+end)/2+1,end,RightMax,RightMin);

    Max = (RightMax > LeftMax) ? RightMax : LeftMax;
    Min = (LeftMin < RightMin) ? LeftMin : RightMin;
    }
    //暴力方法
    void MaxandMin2(int *a,int len,int &max,int &min)
    {
      //if(a == NULL || len <= 0)
    //  cout<<"error!"<<endl;
      assert(len > 0); //if(真) 程序运行；else 报错&&终止程序
       max=a[0];
       min=a[0];
      for(int i(1);i<=len-1;++i)
      {
        if(max < a[i])
    max = a[i];
    if(min > a[i])
    min = a[i];
      }

    }
    // 遍历一遍数组使得下标为偶数的元素较下标为奇数的元素大,再分别求出最大值和最小值
                //比较次数为3*N/2次
    void MaxandMin3(int *a,int len,int &max,int &min)
    {
      if(a == NULL || len<= 0 )
     return;
      for(int i(0);i<len;i+=2)
      {
         if(i<len && a[i] < a[i+1])
    {
      int temp = a[i+1];
    a[i+1] = a[i];
    a[i] = temp;
    }
      }
      max=a[0];
       for(int j(2);j<len;j+=2)
       {
         if(max < a[j])
    {
      max = a[j];
    }
       }
       min = a[1];
       for(int k(3);k<len;k+=2)
       {
         if(min > a[k])
    {
      min = a[k];
    }
       }
    }

    //
    void MaxandMin4(int *a,int len,int &max,int &min)
    {
       if(len > 0 && a != NULL)
       {
           if(len == 1)
      {
        max = min = a[0];
      }
      if(len == 2)
      {
        if(a[0] > a[1])
    {
      max = a[0];
      min = a[1];
    }
      }

      //
      if(a[0] > a[1])
    {
      max = a[0];
      min = a[1];
    }
      else
      {
        max = a[1];
    min = a[0];
      }
    for(int i(2);i<len;i+=2)
       {
         if(i+1 < len && a[i] > a[i+1])
    {
       if(max < a[i])
    {
    max = a[i];
    }
    if(min > a[i+1])
    {
     min = a[i+1];
    }
    }
    else if(i+1 < len && a[i] < a[i+1])
    {
       if(max < a[i+1])
    {
    max = a[i+1];
    }
    if(min > a[i])
    {
     min = a[i];
    }
    }
    else
    {
    if(max < a[i])
    {
          max = a[i];
    }
        if(min > a[i])
    {
          min = a[i];
    }
    }
       }
     }
    }

    int main()
    {
    int a[10]={1,2,3,4,9,8,7,6,5,0};
    int max=0;
    int min =0;
        MaxandMin(a,0,9,max,min);
    cout<<"max="<<max<<endl<<"min="<<min<<endl;
    MaxandMin2(a,10,max,min);
    cout<<"max="<<max<<endl<<"min="<<min<<endl;
    MaxandMin3(a,10,max,min);
    cout<<"max="<<max<<endl<<"min="<<min<<endl;
    MaxandMin4(a,10,max,min);
    cout<<"max="<<max<<endl<<"min="<<min<<endl;
      return 0;
    }