Initialization

• Empty Vector:

std::vector<int> vec;

• Pre-allocate Size:

std::vector<int> vec(10);  // Contains 10 elements, all initialized to 0

• Pre-allocate Size with Value:

std::vector<int> vec(10, 1);  // Contains 10 elements, all initialized to 1

• Initialize from Array:

int arr[] = {1, 2, 3};
std::vector<int> vec(arr, arr + sizeof(arr) / sizeof(int));

• Initialize from Another Vector:

std::vector<int> vec2(vec);

Adding Elements

• Append to End:

vec.push_back(4);

• Insert at Beginning:

vec.insert(vec.begin(), 4);

• Insert at Specific Position:

vec.insert(vec.begin() + 1, 4);

• append vector

vec.insert(vec.end(),vec_2.begin(),vec_2.end())

Access Elements

• Access Last Element:

int last = vec.back();

• Access First Element:

int first = vec.front();

• Access i-th Element (0-based):

int elem = vec[i];

Removing Elements

• Remove Last Element:

vec.pop_back();    ->void

• Remove i-th Element:

vec.erase(vec.begin() + i);

• Remove a Range of Elements:

vec.erase(vec.begin() + i, vec.begin() + j);  // Removes elements from i to j-1

Query Attributes

• Get Vector Size:

size_t size = vec.size();

• Check if Vector is Empty:

bool isEmpty = vec.empty();

Other Common Operations

• Clear Vector:

vec.clear();

• Resize Vector:

vec.resize(20);  // New elements are initialized to 0

• Find Element Position:

std::find(vec.begin(), vec.end(), value) != vec.end()

• Sort Vector:

std::sort(vec.begin(), vec.end());

Examples

#include <iostream>
#include <vector>
#include <algorithm>

int main() {
    std::vector<int> vec = {3, 1, 4, 1, 5, 9, 2, 6, 5};

    // 使用 std::min_element 和 lambda 函数找到最小正整数
    auto it = std::min_element(vec.begin(), vec.end(), [](int a, int b) {
        if (a <= 0) return false;
        if (b <= 0) return true;
        return a < b;
    });

    if (it != vec.end() && *it > 0) {
        std::cout << "最小正整数是：" << *it << std::endl;
    } else {
        std::cout << "没有找到正整数" << std::endl;
    }

    return 0;
}

#include <iostream>
#include <vector>
#include <algorithm>

int main() {
    std::vector<int> vec = {1, 2, 2, 3, 4, 4, 5};

    // 先排序
    std::sort(vec.begin(), vec.end());

    // 使用 std::unique 去重
    auto last = std::unique(vec.begin(), vec.end());

    // 删除多余元素
    vec.erase(last, vec.end());

    // 输出去重后的向量
    for (const auto& elem : vec) {
        std::cout << elem << " ";
    }
    std::cout << std::endl;

    return 0;
}