【笔试练习题】排序算法

测试用的IDE是牛客网：https://www.nowcoder.com/questionTerminal/508f66c6c93d4191ab25151066cb50ef

【1】快速排序

#include <vector>
#include <random>
#include <algorithm>
#include <iostream>
using namespace std;

template<typename T>
T partition(vector<T> &v, int l, int r){
    // 随机化排序的中点，优化性能
    default_random_engine e;
    int rad = e()%(r - l) + l;
    swap(v[l], v[rad]);
    
    int p = l;
    while(l < r){
        while(r > l && v[r] >= v[p]){
            r--;
        }
        while(l < r && v[l] <= v[p]){
            l++;
        }
        if(v[r] < v[l]){
            swap(v[l], v[r]);
        }
    }
    swap(v[p], v[r]);
    return r;
}
template<typename T>
void quick_sort(vector<T> &v, const int l, const int r)
{
    if(l >= r){
        return;
    }
    int p = partition(v, l, r);
    quick_sort(v, l, p - 1);
    quick_sort(v, p + 1, r);
}
template<typename T>
void my_sort(vector<T> &v){
    quick_sort(v, 0, v.size() - 1);
    for(int i = 0; i < v.size(); ++i){
        cout << v[i] << " ";
    }
    cout << endl;
}
int main(){
    int n;
    while(cin >> n){
        vector<int> v;
        v.reserve(n);
        for(int i = 0; i < n; ++i)
        {
            int tmp;
            cin >> tmp;
            v.push_back(tmp);
        }
        my_sort(v);
    }
}

【2】堆排序

STL中有对堆操作的函数：https://blog.youkuaiyun.com/cillyb/article/details/52224330

#include <vector>
#include <algorithm>
#include <iostream>
using namespace std;

template<typename T>
void heap_shiftUp(vector<T> &v, int begin, int position) // 这是一个大顶堆,上浮
{
	if(position == begin)
		return;
	T value = v[position];
	int parent = (position - 1)/2;
	int node = position;
	while(node > begin && value > v[parent]){
		v[node] = v[parent];
		node = parent;
		parent = (node - 1)/2;
	}
	v[node] = value;
}

template<typename T>
int get_child(vector<T> &v, int end, int node)
{
	int child1 = (node + 1)*2;
	int child2 = child1 - 1;
	int child;
	if(child2 >= end){
	 	return node;
	}
	else if(child1 >= end){
		child = child2;
	}
	else child = (v[child1] > v[child2]) ? child1 : child2;
	return child;
}

template<typename T>
void heap_shiftDown(vector<T> &v, int end, int position) // 这是一个大顶堆, 下沉
{
	T value = v[position];
	int node = position;
	int child = get_child(v, end, node);
	while(node < child && value < v[child]){
		v[node] = v[child];
		node = child;
		child = get_child(v, end, node);
	}
	v[node] = value;
}

template<typename T>
void make_heap(vector<T> &v)
{
	for(unsigned int i = 1; i < v.size(); ++i){
		heap_shiftUp(v, 0, i);
	}

}

template<typename T>
void heap_sort(vector<T> &v){
	for(int i = v.size() - 1; i > 0; i--){
		swap(v[i], v[0]);
		heap_shiftDown(v, i, 0);
	}
}

template<typename T>
void my_sort(vector<T> &v){
    make_heap(v);
    heap_sort(v);
    for(int i = 0; i < v.size(); ++i){
        cout << v[i] << " ";
    }
    cout << endl;
}

int main(){
    int n;
    while(cin >> n){
        vector<int> v;
        v.reserve(n);
        for(int i = 0; i < n; ++i)
        {
            int tmp;
            cin >> tmp;
            v.push_back(tmp);
        }
        my_sort(v);
    }
}