求数组中的最大值和次大值

基本方法 使用sort函数

#include<iostream> 
#include<algorithm>

using namespace std;
#define N 5
int main(){
	int a[N] = {5,1,3,6,2}; 
	sort(a,a+5);
	cout<<a[4]<<" "<<a[3]<<endl;
}

使用打擂台 

#include<iostream>
#define N 5
int main(){
	int a[N] = {5,1,3,6,2};
	int max1 = 0;//最大值 
	int max2 = 0;//次大值 
	for(int i=0;i<N;i++){
		//数字比最大值还大，将最大值给次大值 
		if(a[i]>max1){
			max2 = max1;
			max1 = a[i];
		}
		else if(a[i]>max2){
			max2 = a[i];
		}
	}
	std::cout<<max1<<" "<<max2<<std::endl;
}

使用分治算法

void max1max2(int a[],int low,int high,int &max1,int &max2){
    if(low>high) return ;
    //剩下一个数 
	else if(low == high) {
		max1 = a[low];
		max2 = INF;
	}
	//剩下两个数 
	else if(low == high - 1){
		max1 = max(a[low],a[high]) ;
		max2 = min(a[low],a[high]);
	}
	//分解 
	else {
	int mid = (high+low)/2;
	int leftmax1, leftmax2;
	max1max2(a,low,mid,leftmax1,leftmax2);
	int rightmax1,rightmax2;
	max1max2(a, mid+1,high,rightmax1,rightmax2);
	if(leftmax1>rightmax1){
		max1 = leftmax1;
		max2 = max(leftmax2,rightmax1);
	}
	
	else {
		max1 = rightmax1;
		max2 = max(leftmax1,rightmax2);
	    }
    }
}