vector
- Vectors 是一動態陣列，可以自動的調整其容器的容量。
- Vector 的元素被儲存在連續的記憶體空間，所以可以使用迭代器(iterators)來進行存取。
- 在 vectors 中，元素是被插入在尾端的，插入尾端的時間取決於是否須進行容量的調整。
- 在 vectors 中，刪除尾端元素的時間複雜度則是固定的\(O(1)\)，因為不會發生容量調整。
- 在 vectors 的前端或中間插入元素或是清除元素，時間的複雜度都是\(O(n)\)。
迭代器(Iterators)
1. vec.begin()
- 回傳指向 vector 中第一個元素的迭代器 (vec[0])
2. vec.end()
- 回傳指向 vector 中最後一個元素之後一個的迭代器 (vec[n+1])
3. vec.rbegin()
- 回傳指向 vector 中最後一個元素的反向迭代器 (vec[n])
4. vec.rend()
- 回傳指向 vector 中第一個元素之前一個的反向迭代器 (vec[-1])
5. vec.cbegin()
- 回傳指向 vector 中第一個元素的常數迭代器 (vec[0])
6. vec.cend()
- 回傳指向 vector 中最後一個元素之後一個的常數迭代器 (vec[n+1])
7. vec.crbegin()
- 回傳指向 vector 中最後一個元素的反向常數迭代器 (vec[n])
8. vec.crend()
- 回傳指向 vector 中第一個元素之前一個的反向常數迭代器 (vec[-1])
#include <bits/stdc++.h>
using namespace std;
int main(){
int arr[] = {1,1,2,3,5,8,13,21,34,55};
int n = sizeof(arr)/sizeof(arr[0]);
vector<int> vec(arr, arr + n); // initialize with array
cout << "Output of begin() and end(): ";
for (auto i = vec.begin(); i != vec.end(); ++i) cout << *i << " ";
cout << "\nOutput of rbegin() and rend(): ";
for (auto i = vec.rbegin(); i != vec.rend(); ++i) cout << *i << " ";
cout << "\nOutput of cbegin() and cend(): ";
for (auto i = vec.cbegin(); i != vec.cend(); ++i) cout << *i << " ";
cout << "\nOutput of crbegin() and crend(): ";
for (auto i = vec.crbegin(); i != vec.crend(); ++i) cout << *i << " ";
return 0;
}
結果：
Output of begin() and end(): 1 1 2 3 5 8 13 21 34 55
Output of rbegin() and rend(): 55 34 21 13 8 5 3 2 1 1
Output of cbegin() and cend(): 1 1 2 3 5 8 13 21 34 55
Output of crbegin() and crend(): 55 34 21 13 8 5 3 2 1 1
容量(capacity)
1. vec.size()
- 回傳 vector 的元素數量
2. vec.max_size()
- 回傳 vector 可以持有的最大元素數量
3. vec.capacity()
- 回傳 vector 當前被分配到的儲存空間，以元素數目表示
4. vec.empty()
- 回傳容器是否沒有元素的
5. vec.shrink_to_fit()
- 將容器的容量縮減到剛好符合它的元素數量，並丟棄所有超出容量的元素
6. vec.resize(int n)
- 將容器的容量重新調整到
n個元素的大小
7. vec.reserve(int n)
- 將容器的容量重新調整到至少可以容納
n個元素的大小。
#include <bits/stdc++.h>
#include "print.cc"
using namespace std;
int main(){
vector<int> vec;
for (int i = 0; i <= 12; ++i)
vec.push_back(i);
cout << "Max_size: " << vec.max_size() << "\n";
cout << "==================================\n";
cout << "Initial" << "\n";
cout << "Size: " << vec.size() << "\n";
cout << "Capacity: " << vec.capacity() << "\n";
print(vec);
cout << "==================================\n";
vec.resize(8);
cout << "After resize(8)" << "\n";
cout << "Size: " << vec.size() << "\n";
cout << "Capacity: " << vec.capacity() << "\n";
print(vec);
cout << "==================================\n";
vec.shrink_to_fit();
cout << "After fitting" << "\n";
cout << "Size: " << vec.size() << "\n";
cout << "Capacity: " << vec.capacity() << "\n";
print(vec);
cout << "==================================\n";
vec.reserve(20);
cout << "After reserve(20)" << "\n";
cout << "Size: " << vec.size() << "\n";
cout << "Capacity: " << vec.capacity() << "\n";
print(vec);
cout << "==================================\n";
cout << "If the vector is empty: ";
vec.empty() ? (cout << "Empty") : (cout << "Not empty") << "\n";
return 0;
}
結果：
Max_size: 4611686018427387903
==================================
Initial
Size: 13
Capacity: 16
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
==================================
After resize(8)
Size: 8
Capacity: 16
[0, 1, 2, 3, 4, 5, 6, 7]
==================================
After fitting
Size: 8
Capacity: 8
[0, 1, 2, 3, 4, 5, 6, 7]
==================================
After reserve(20)
Size: 8
Capacity: 20
[0, 1, 2, 3, 4, 5, 6, 7]
==================================
If the vector is empty: Not empty
存取元素(access elements)
1. vec[int n]
- 回傳
n指標位置的值
2. at(int n)
- 回傳
n指標位置的位
3. front()
- 回傳第一個元素的值
4. back()
- 回傳最後一個元素的值
5. data()
- 回傳一個直接的指標指向 vector 的記憶體位置
#include <bits/stdc++.h>
#include "print.cc"
using namespace std;
int main(){
int arr[] = {0, 1, 2, 3, 4, 5, 6, 7};
int n = sizeof(arr)/sizeof(arr[0]);
vector<int> vec(arr, arr + n);
print(vec);
cout << "vec[2]: " << vec[2] << "\n";
cout << "vec.at(4): " << vec.at(4) << "\n";
cout << "vec.front(): " << vec.front() << "\n";
cout << "vec.back(): " << vec.back() << "\n";
int* pos = vec.data();
for (int* i = pos; i != pos + vec.size(); i++){
cout << *i << " ";
}
return 0;
}
結果
[0, 1, 2, 3, 4, 5, 6, 7]
vec[2]: 2
vec.at(4): 4
vec.front(): 0
vec.back(): 7
0 1 2 3 4 5 6 7
修改元素(modify elements)
1. assign(int n, E val)
- 指派新的值到 vector 中，並取代舊的值
2. push_back(E val)
- 將新的值加到 vector 的尾端
3. pop_back()
- 將 vector 的尾端的值取出並移除
4. insert(iterator it, E val)
- 在 vector 的指定位置加入新的值
5. erase(iterator it)
- 移除 vector 指定位置的移
6. v1.swap(v2)
- 交換兩個 vector 的值
7. vec.clear()
- 清除 vector 的所有值
#include <bits/stdc++.h>
#include "print.cc"
using namespace std;
int main(){
vector<int> vec;
cout << "After assign(5, 10): \n";
vec.assign(5, 10);
print(vec);
cout << "After push_back(15): \n";
vec.push_back(15);
print(vec);
int n = vec.size();
cout << "The last element is: " << vec.back() << "\n";
cout << "After pop_back(): \n";
vec.pop_back();
print(vec);
cout << "After insert(vec.begin(), 5): \n";
vec.insert(vec.begin(), 5);
print(vec);
cout << "After erase(vec.begin()): \n";
vec.erase(vec.begin());
print(vec);
vec.clear();
cout << "Vector size after clear(): " << vec.size() << "\n";
vector<int> v1, v2;
v1.push_back(1);
v1.push_back(2);
v2.push_back(3);
v2.push_back(4);
cout << "Vector 1: ";
print(v1);
cout << "Vector 2: ";
print(v2);
// Swaps v1 and v2
v1.swap(v2);
cout << "After Swap \nVector 1: ";
print(v1);
cout << "Vector 2: ";
print(v2);
return 0;
}
結果
After assign(5, 10):
[10, 10, 10, 10, 10]
After push_back(15):
[10, 10, 10, 10, 10, 15]
The last element is: 15
After pop_back():
[10, 10, 10, 10, 10]
After insert(vec.begin(), 5):
[5, 10, 10, 10, 10, 10]
After erase(vec.begin()):
[10, 10, 10, 10, 10]
Vector size after clear(): 0
Vector 1: [1, 2]
Vector 2: [3, 4]
After Swap
Vector 1: [3, 4]
Vector 2: [1, 2]
- 你可能會想繼續閱讀…