算法导论+编程之美，查找数组中最大值和最小值

查找数组中最大值和最小值，

方法一：分治法，一分为二，分别查找子数组中最大值和最小值，合并时取两个子数组的较大者和较小者。f(n) = 2f(n-1)+2；f(n)=1.5n-2；

方法二：将数组中元素每两个一组，先比较每组中两个元素，让较大者与最大值比较，较小者与最小值比较，每组比较3次，共需比较次数为1+1.5（n-2）=1.5n-2；

从空间角度看，非递归的方法二更简单；

#include <iostream>

using namespace std;

void FindMaxAndMin(int num[],int l,int r,int &minNum,int &maxNum);
void FindMaxAndMin2(int num[],int n,int &minNum,int &maxNum);

int main()
{
int n = 6;
int num[] = {6,5,8,3,9,7};
int minNum,maxNum;

FindMaxAndMin(num,0,n-1,minNum,maxNum);
for(int i=0 ; i<n ; i++){
cout << num[i] << " ";
}
cout << endl;

cout << minNum << " " <<maxNum<< endl;

FindMaxAndMin2(num,n,minNum,maxNum);
cout << minNum << " " <<maxNum<< endl;

return 0;
}
void FindMaxAndMin2(int num[],int n,int &minNum,int &maxNum)
{
int i = 0;

if(n <= 0){
minNum = -1;
maxNum = -1;
return ;
}
if(n%2 == 1){//奇数个数
minNum = num[0];
maxNum = num[0];
i = 1;
}
else{//偶数个数
if(num[0] > num[1]){
maxNum = num[0];
minNum = num[1];
}
else{
maxNum = num[1];
minNum = num[0];
}
i = 2;
}
for( ; i<n ; i+=2){
if(num[i]>num[i+1]){
if(maxNum < num[i]){
maxNum = num[i];
}
if(minNum > num[i+1]){
minNum = num[i+1];
}
}
}

}

void FindMaxAndMin(int num[],int l,int r,int &minNum,int &maxNum)
{
int minl,maxl,minr,maxr;

if(r - l == 0){
minNum = num[r];
maxNum = num[r];
return ;
}
if(r - l == 1){
if(num[r] > num[l]){
maxNum = num[r];
minNum = num[l];
}
else{
maxNum = num[l];
minNum = num[r];
}
return ;
}
FindMaxAndMin(num,l,(l+r)/2,minl,maxl);
FindMaxAndMin(num,1+(l+r)/2,r,minr,maxr);
//merge
if(minl < minr){
minNum = minl;
}
else{
minNum = minr;
}
if(maxl > maxr){
maxNum = maxl;
}
else{
maxNum = maxr;
}

}