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笔记、记录、总结

STL基础部分

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摘要：基础部分、string、vector、queue、stack、set、deque、list…

string

输入输出字符串

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#include <bits/stdc++.h>
using namespace std;

int main(){
//    string s = "12312hello world...";
    string s;
    getline(cin, s);//输入字符串
    cout<<s;
    return 0;
}
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21314 hello woefsdcsd
21314 hello woefsdcsd
Process finished with exit code 0

字符串拼凑

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#include <bits/stdc++.h>
using namespace std;

int main(){
//    string s = "12312hello world...";
    string s;
    s += "shda s";
    s += "shda s";
    s += '5';

    cout<<s;
    return 0;
}
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shda sshda s5
Process finished with exit code 0

排序

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#include <bits/stdc++.h>

using namespace std;

int main() {
    string s = "1523525431873";
    sort(s.begin(), s.end());
    cout << s;
    return 0;
}
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1122333455578
Process finished with exit code 0
  • s.begin(), s.end()是迭代器，可以看成是指针
  • 如果要访问最后一个字符，应该是*(--s.end())

erase删除

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#include <bits/stdc++.h>

using namespace std;

int main() {
    string s = "1523525431873";
    s.erase(s.begin());
    s.erase(--s.end());
    cout << s;
    return 0;
}
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52352543187
Process finished with exit code 0

substr取子串

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#include <bits/stdc++.h>

using namespace std;

int main() {
    string s = "1523525431873";
    s = s.substr(2, 3);//从索引为2开始取，往后取三个
    cout << s;
    s = "1523525431873";
    s = s.substr(6, -1);//从索引为6开始取，直到最后一个
    cout << endl << s;
    return 0;
}
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235
5431873
Process finished with exit code 0

几种循环方式

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#include <bits/stdc++.h>

using namespace std;

int main() {
    string s = "1523525431873";
    for (int i = 0; i < s.length(); ++i)
        cout << s[i];

    cout << '\n';
    for (string::iterator iter = s.begin(); iter != s.end(); iter++)
        cout << *iter;
    
    cout << '\n';
    for (auto i : s)
        cout << i;


    cout << endl << s;
    return 0;
}
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1523525431873
1523525431873
1523525431873
1523525431873
Process finished with exit code 0

vector

初始化、打印

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#include <bits/stdc++.h>

using namespace std;

int main() {
    vector<int> v(3, 1);//初始化3个1
    vector<int> v1(3);//初始化3个0
    vector<int> v2{1, 2, 3, 4, 5};//初始化5个数
    for (auto x:v)cout << x;
    cout << '\n';
    for (auto x:v1)cout << x;
    cout << '\n';
    for (auto x:v2)cout << x;
    cout << '\n';
    return 0;
}
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111
000
12345

Process finished with exit code 0

取元素 []或者at()

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#include <bits/stdc++.h>

using namespace std;

int main() {
    vector<int> v{1, 2, 3, 4, 5};//初始化5个数
    //取某个元素
    cout<<v[2];//取索引为2 元素
    cout<<v.at(4);//取索引为4的元素
    return 0;
}

追加push_back

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#include <bits/stdc++.h>

using namespace std;

int main() {
    vector<int> v{1, 2, 3, 4, 5};//初始化5个数
    v.push_back(7);
    v.push_back(7);
    v.push_back(7);
    for (auto x:v) cout << x;
    return 0;
}
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12345777
Process finished with exit code 0

resize重置大小，后面补0

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#include <bits/stdc++.h>

using namespace std;

int main() {
    vector<int> v{1, 2, 3, 4, 5};//初始化5个数
    v.push_back(7);
    v.push_back(7);
    v.push_back(7);
    for (auto x:v) cout << x;
    v.resize(20);//进行重置大小，后面补0
    cout<<endl;
    for (auto x:v) cout << x;
    return 0;
}
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12345777
12345777000000000000
Process finished with exit code 0

erase删除，在vector中的复杂度为O(n)

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#include <bits/stdc++.h>

using namespace std;

int main() {
    vector<int> v{1, 2, 3, 4, 5};//初始化5个数
    v.push_back(7);
    v.push_back(7);
    v.push_back(7);
    for (auto x:v) cout << x;
    cout<<endl;
    //删除,在这里的复杂度为O(n)
    v.erase(v.begin());
    v.erase(--v.end());
    for (auto x:v) cout << x;

    return 0;
}
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12345777
234577
Process finished with exit code 0

front(),back()

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#include <bits/stdc++.h>

using namespace std;

int main() {
    vector<int> v{1, 2, 3, 4, 5};//初始化5个数
    v.push_back(7);
    v.push_back(7);
    v.push_back(7);
    for (auto x:v) cout << x;
    cout << endl;
    //取元素
    cout << v.front() << ' ' << v.back() << endl;
    cout << *v.begin() << ' ' << *(--v.end()) << ' ' << v[v.size() - 1];
    return 0;
}
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12345777
1 7
1 7 7
Process finished with exit code 0

排序sort

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#include <bits/stdc++.h>

using namespace std;

int main() {
    vector<int> v{1, 55, 15, 4, 25};//初始化5个数
    v.push_back(7);
    v.push_back(7);
    v.push_back(7);
    for (auto x:v) cout << x << ' ';
    cout << endl;

    sort(v.begin(), v.end());
    for (auto x:v) cout << x << ' ';
    cout << endl;

    sort(v.rbegin(), v.rend());
    for (auto x:v) cout << x << ' ';
    cout << endl;

    return 0;
}
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1 55 15 4 25 7 7 7
1 4 7 7 7 15 25 55
55 25 15 7 7 7 4 1

Process finished with exit code 0
  • 从大到小还可以用
    sort(v.begin(), v.end(), greater<>());

    循环与string的类似

  • 用的较多的是for (auto x:v) cout << x << ' ';

stack

初始化

  • 一般刷算法题都直接这样写 stack<int> s;
  • 如果不用<bits/stdc++.h>,那要用<stack>
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    #include <bits/stdc++.h>
    using namespace std;
    int main() {
        stack<int> s;
        cout << endl;
        return 0;
    }

    push, pop, top

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    #include <bits/stdc++.h>

    using namespace std;

    int main() {
        stack<int> s;
        s.push(2);
        s.push(1);
        s.push(3);
        cout << s.top();
        s.pop();
        cout << s.top();
        return 0;
    }
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  • push 入栈
  • pop出栈
  • top取栈顶
  • size取长度
  • cout << s.empty(); 是空就返回1，否则为0

    十进制转二进制

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    #include <bits/stdc++.h>

    using namespace std;

    int tenToTwo(int decimal) {
        stack<int> s;
        int res = 0;
        while (decimal != 0) {
            s.push(decimal % 2);
            decimal /= 2;
        }
        while (!s.empty()) {
            res = res * 10 + s.top();
            s.pop();
        }
        return res;
    }

    int main() {
        cout << tenToTwo(11);
        return 0;
    }
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    1011
    Process finished with exit code 0

    逆序输出句子单词

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    #include <bits/stdc++.h>
    using namespace std;
    int main() {
        stringstream ss;
        string str;
        getline(cin, str);
        ss << str;
        stack<string> s;
        while (ss >> str) {
            s.push(str);
        }
        while (!s.empty()) {
            cout << s.top();
            if (s.size() != 1) cout << ' ';
            s.pop();
        }
        return 0;
    }

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    we are young man
    man young are we
    Process finished with exit code 0

    字符串转化为数字

    方法一

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#include <bits/stdc++.h>
using namespace std;
int main() {
    stringstream ss;
    string str = "12455";
    //把字符串转换为数字
    ss << str;//先把“12345”流入ss
    int num;
    ss >> num;//再从ss流入整型num
    cout << num;
    return 0;
}

12455
Process finished with exit code 0

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### 方法二
​```c++
int main() {
    stringstream ss;
    string str = "12455";
    //把字符串转换为数字
    int num = stoi(str);
    cout << num;
    return 0;
}
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12455
Process finished with exit code 0

数字转换为字符串

方法一

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#include <bits/stdc++.h>
using namespace std;

int main() {
    stringstream ss;
    string str;
    //数字转化为字符串
    int num = 12556;
    ss << num;
    ss >> str;
    cout << str;
    return 0;
}
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12556
Process finished with exit code 0

方法二

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#include <bits/stdc++.h>
using namespace std;

int main() {
    stringstream ss;
    string str;
    //数字转化为字符串
    int num = 12556;
    str = to_string(num);
    cout << str;
    return 0;
}
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12556

queue

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#include <bits/stdc++.h>
using namespace std;

int main() {
    queue<int> q;
    q.push(4);
    q.push(3);
    q.push(5);
    cout<<q.size()<<' '<<q.front();
    return 0;
}
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map 和 unordered_map

  • map: 有序的，底层是树状结构
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    #include <bits/stdc++.h>

    using namespace std;

    int main() {
        map<int, int> dict;
        dict[1] = 2;
        dict[2] = 0;
        dict[4] = 12;
        //打印
        for (auto item: dict)
            cout << item.first << ' ' << item.second << endl;
        //另一种打印方式
        for (auto iterator = dict.begin(); iterator != dict.end(); iterator++)
            cout << iterator->first << ' ' << iterator->second << endl;
        return 0;
    }
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    1 2
    2 0
    4 12
    1 2
    2 0
    4 12

    Process finished with exit code 0
  • unordered——map：无序的，底层是哈希结构
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#include <bits/stdc++.h>

using namespace std;

int main() {
    unordered_map<int, int> dict;
    dict[1] = 2;
    dict[2] = 0;
    dict[4] = 12;
    //打印
    for (auto item: dict)
        cout << item.first << ' ' << item.second << endl;
    //另一种打印方式
    for (auto iterator = dict.begin(); iterator != dict.end(); iterator++)
        cout << iterator->first << ' ' << iterator->second << endl;
    return 0;
}
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4 12
1 2
2 0
4 12
1 2
2 0
Process finished with exit code 0

  • 打印出来是无序的

    set

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    #include <bits/stdc++.h>

    using namespace std;


    int main() {
        unordered_set<int> s;
    //    set<int> s;
        s.insert(2);
        s.insert(2);
        s.insert(3);

        cout << s.size();
        for (auto i:s)
            cout << i;
        return 0;
    }
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    Process finished with exit code 0

    deque

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    #include <bits/stdc++.h>
    using namespace std;

    int main() {
        deque<int> deque;
        deque.push_back(1);
        deque.push_back(2);
        deque.push_front(3);
        deque.push_front(4);
        for (auto i: deque)
            cout << i;
        deque.pop_back();
        deque.pop_front();
        cout<<endl;
        for (auto i: deque)
            cout << i;
        return 0;
    }
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    4312
    31
    Process finished with exit code 0

    可以排序

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    #include <bits/stdc++.h>

    using namespace std;


    int main() {
        deque<int> deque;
        deque.push_back(1);
        deque.push_back(2);
        deque.push_front(3);
        deque.push_front(4);
        for (auto i: deque)
            cout << i;
        sort(deque.begin(), deque.end());
        cout<<endl;
        for (auto i: deque)
            cout << i;
        return 0;
    }
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    4312
    1234
    Process finished with exit code 0

    list

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    #include <bits/stdc++.h>

    using namespace std;


    int main() {
        list<int> list;
        list.push_front(2);
        list.push_front(3);
        list.push_back(4);
        list.push_back(1);
        for (auto i: list)
            cout << i << ' ';
        cout << endl;
        //插入
        list.insert(++list.begin(), 99);
        for (auto i: list)
            cout << i << ' ';
        cout << endl;
        //里面的值
        list.remove(3);
        for (auto i: list)
            cout << i << ' ';
        return 0;
    }
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    3 2 4 1
    3 99 2 4 1
    99 2 4 1
    Process finished with exit code 0
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