归并排序 mergesort

#include <iostream>
#include <vector>
#include <stdlib.h>
#include <chrono>
#include <cmath>
#include <algorithm>
template <typename T> 
inline void swap(T * t1, T * t2) {
    T tmp = *t1;
    *t1 = *t2;
    *t2 = tmp;
}

template <typename T>
void mergesort(std::vector<T> & vec) {
    if (vec.size() == 1) {
        return;
    }
    if (vec.size() == 2) {
        if(vec[0] > vec[1]) {
            swap(&vec[0], &vec[1]);
        }
        return;
    }
    auto Index = (vec.size() - 1)/ 2;
    std::vector<T> vec1 = {vec.begin(), vec.begin() + Index};
    std::vector<T> vec2 = {vec.begin() + Index, vec.end()};
    mergesort(vec1);
    mergesort(vec2);
    // insert
    int index1 = 0, index2 = 0, index = 0;
    while(true) {
        if(index == vec.size() ) {
            break;
        }
        if(index1 == vec1.size()) {
            while(index2 < vec2.size()) {
                vec[index++] = vec2[index2++];
            }
        }
        else if(index2 == vec2.size()) {
            while(index1 < vec1.size()) {
                vec[index++] = vec1[index1++];
            }
        }
        else if(vec1[index1] < vec2[index2]) {
            vec[index++] = vec1[index1++];
        } else {
            vec[index++] = vec2[index2++];
        }
    }
}


void genertor(std::vector<int> &vec, int max) {
    for (auto & item : vec) {
        item = rand() % max;
    }
}

int main() {
    std::vector<int> vec;
    auto size = 10;
    vec.resize(size);
    genertor(vec, size);
    std::cout << "before sort: ";
    std::for_each(vec.cbegin(), vec.cend(), [](const int & n) { std::cout << " " << n;});
    auto startTime = std::chrono::high_resolution_clock::now();
    mergesort(vec);
    auto endTime = std::chrono::high_resolution_clock::now();
    std::chrono::duration<double, std::milli> diffTime = endTime - startTime;
    std::cout << std::endl << "after sort: ";
    std::for_each(vec.cbegin(), vec.cend(), [](const int & n) { std::cout << " " << n;});
    std::cout << std::endl << "size: " << size << ", quick sort timecost = " << diffTime.count() << "ms" << std::endl;
    return 0;
}

运行

before sort:  7 9 3 8 0 2 4 8 3 9
after sort:  0 2 3 3 4 7 8 8 9 9
size: 10, quick sort timecost = 0.006777ms

标签：std,mergesort,归并,++,vec2,vec,vec1,排序,size
来源： https://blog.csdn.net/u014789533/article/details/120166416