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]

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vector#

迭代器(Iterators)#

1. vec.begin()#

2. vec.end()#

3. vec.rbegin()#

4. vec.rend()#

5. vec.cbegin()#

6. vec.cend()#

7. vec.crbegin()#

8. vec.crend()#

容量(capacity)#

1. vec.size()#

2. vec.max_size()#

3. vec.capacity()#

4. vec.empty()#

5. vec.shrink_to_fit()#

6. vec.resize(int n)#

7. vec.reserve(int n)#

存取元素(access elements)#

1. vec[int n]#

2. at(int n)#

3. front()#

4. back()#

5. data()#

修改元素(modify elements)#

1. assign(int n, E val)#

2. push_back(E val)#

3. pop_back()#

4. insert(iterator it, E val)#

5. erase(iterator it)#

6. v1.swap(v2)#

7. vec.clear()#

vector

迭代器(Iterators)

1. vec.begin()

2. vec.end()

3. vec.rbegin()

4. vec.rend()

5. vec.cbegin()

6. vec.cend()

7. vec.crbegin()

8. vec.crend()

容量(capacity)

1. vec.size()

2. vec.max_size()

3. vec.capacity()

4. vec.empty()

5. vec.shrink_to_fit()

6. vec.resize(int n)

7. vec.reserve(int n)

存取元素(access elements)

1. vec[int n]

2. at(int n)

3. front()

4. back()

5. data()

修改元素(modify elements)

1. assign(int n, E val)

2. push_back(E val)

3. pop_back()

4. insert(iterator it, E val)

5. erase(iterator it)

6. v1.swap(v2)

7. vec.clear()