算法之归并排序(mergesort)
作者:互联网
算法之归并排序(mergesort)
情况一、 两个有序(升序)的数组归并为一个有序数组
时间复杂度O(N)
原理
通过指针法:先比较两数组的初始位置的数据大小,比较小的数据放入一个最终的数组中,并且此数组向后移位,较小数据的数组也向后移动。
#include <vector>
#include <iostream>
#include <iterator>
using namespace std;
class Solution{
public:
const vector<int> mergesort(vector<int>& nums , vector<int>& vect){
vector<int> ans;
auto nums_it = nums.begin();
auto vect_it = vect.begin();
while(nums_it != nums.end() && vect_it != vect.end()){
if(*nums_it > *vect_it){
ans.push_back(*vect_it);
vect_it++;
}
else {
ans.push_back(*nums_it);
nums_it++;
}
}
if(nums_it == nums.end()){
for(; vect_it != vect.end(); vect_it++){
ans.push_back(*vect_it);
}
}
else {
for(; nums_it != nums.end(); nums_it++){
ans.push_back(*nums_it);
}
}
return ans;
}
};
int main(){
Solution sl;
vector<int> nums{4,5,6,11,32,55,77,88};
vector<int> vect{6,9,44,222,434,555};
nums = sl.mergesort(nums,vect);
for(auto i : nums)
cout << i <<" ";
cout << endl;
}
情况二、 将一个无序数组归并为一个有序数组
时间复杂度O(N)
原理
利用递归的方法,采用分治的思想进行排序,每一次划分一半,到最后调用两个有序数组的归并,先归并3 和 1,
#include <vector>
#include <iostream>
#include <iterator>
using namespace std;
class Solution{
public:
void mergesort(vector<int>& nums , vector<int>& temp, int left , int mid , int right){
//[left,mid) -- 一个有序数组
//[mid , right] -- 一个有序数组
int index = 0;
vector<int> comp1;
vector<int> comp2;
index = left;
for(int i = left; i < mid; i++)
comp1.push_back(nums[i]);
for(int i = mid; i <= right; i++)
comp2.push_back(nums[i]);
auto comp1_it = comp1.begin();
auto comp2_it = comp2.begin();
while(comp1_it != comp1.end() && comp2_it != comp2.end()){
if(*comp1_it > *comp2_it){
temp[index++]= *comp2_it;
comp2_it++;
}
else {
temp[index++]= *comp1_it;
comp1_it++;
}
}
if(comp1_it == comp1.end()){
for(; comp2_it != comp2.end(); comp2_it++){
temp[index++]= *comp2_it;
}
}
else {
for(; comp1_it != comp1.end(); comp1_it++){
temp[index++]= *comp1_it;
}
}
// 将temp 拷到 nums 对应位置
for(int i = left ; i <= right ; i++){
nums[i] = temp[i];
}
}
void Msort(vector<int>& nums , vector<int> temp , int left , int right){
//递归结束条件
if(left >= right)
return;
int mid = (left + right) >> 1;
Msort(nums, temp, left,mid); // 分治左半边数组
Msort(nums, temp, mid+1, right); // 分治右半边数组
mergesort(nums,temp,left,mid+1,right); // 归并左右两边数组
}
};
int main(){
Solution sl;
vector<int> nums{5,2,6,88,32,14,65,77,3,1,4,7,8,99,90};
vector<int> temp = nums;
int left = 0;
int right = nums.size() - 1 ;
sl.Msort(nums,temp,left,right);
for(auto i : nums)
cout << i <<" ";
cout << endl;
}
标签:mergesort,归并,temp,nums,int,++,vect,vector,排序 来源: https://blog.csdn.net/WRRRRRR5/article/details/120103853