C++ STL编程 vector空间预留、vector高效删除、vector数据排序、vector代码练习

vector空间预留，作用是避免申请每次申请内存，提高运行效率。

对应的接口是 vector.reverse()

vector的高效删除，对应的代码见下，一个时间复杂度是n，一个时间复杂度是1

#include<iostream>
#include<vector>using namespace std;void removeal(vector<int>& v, int index) {v.erase(v.begin() + index); // 时间复杂度是n
}void remove2(vector<int>& v, int index) {swap(v[index], v.back()); // 时间复杂度为1v.pop_back();
}void printVector(vector<int>& v) {for (int i = 0; i < v.size(); ++i) {cout << v[i] << " ";}cout << endl;
}int main() {vector<int> v;cout << "r1: ";for (int i = 0; i < 150006; ++i) {v.push_back(i);}for (int i = 0; i < 150000; ++i) {removeal(v, 4);}	cout << "r1~end";//printVector(v);cout << "r2: ";for (int i = 0; i < 150006; ++i) {v.push_back(i);}for (int i = 0; i < 150000; ++i) {remove2(v, 4);}cout << "r2~end()"; //printVector(v);return 0;
}

vector数据排序，代码见下：

#include<iostream>
#include<algorithm>
#include<vector>using namespace std;void printVector(const vector<int>& v) {for (int i = 0; i < v.size(); ++i) {cout << v[i] << " ";}cout << endl;
}bool cmp(int a, int b) {return a > b;
}int main() {vector<int> v = { 2, 3, 9, 5, 6, 7 };sort(v.begin(), v.end(), cmp);// 这个是默认从小到大排序，可以加个cmp就可以告诉他咋排序printVector(v);
}

代码练习，对应力扣，数组串联，代码见下

class Solution {
public:vector<int> getConcatenation(vector<int>& nums) {int n = nums.size();vector<int> ans(nums);ans.resize(2*n);for(int i=0; i<n; ++i){ans[i+n] = nums[i];}return ans;}
};