[C++知识库]算法模板 字符串

反转字符串
https://leetcode-cn.com/problems/reverse-string/

class Solution {
public:
    void swap(char& a,char& b)
    {
        char temp=a;
        a=b;
        b=temp;
    }
    void reverseString(vector<char>& s) {
            if(s.size()==1) return;
            for(int i=0,j=s.size()-1;i<=(s.size()-2)/2;i++,j--)
            {
                swap(s[i],s[j]);
            }
    }
};

反转字符串II
https://leetcode-cn.com/problems/reverse-string-ii/

class Solution {
public:
    void swap(char& a,char& b)
    {
        char temp=a;
        a=b;
        b=temp;
    }
    string reverseStr(string s, int k) {
        int index=-1;
        while(index+2*k<=s.size()-1)
        {
            index+=2*k;
            for(int i=index-2*k+1,j=index-k;i<j; i++,j--)
            {
                swap(s[i],s[j]);
            }
        }
        int len=s.size()-1-index;
        if(len<k)
        {
            for(int i=index+1,j=s.size()-1;i<j;i++,j--)
            {
                swap(s[i],s[j]);
            }
        }
        else if(len>=k&&len<2*k)
        {
            for(int i=index+1,j=index+k;i<j;i++,j--)
            {
                swap(s[i],s[j]);
            }
        }
        return s;
    }
};

翻转字符串里的单词
https://leetcode-cn.com/problems/reverse-words-in-a-string/

class Solution {
public:
    void trim(string& s)
    {
        //字符串长度为1，不用处理
        if(s.size()==1) return;

        int slow=0,fast=0;
        //去除前面的空格
        while(s[fast]==' ')
        {
            fast++;
        }
        while(fast<=s.size()-1)
        {
            if(s[fast]==' '&&s[fast-1]==' ')
            {
                fast++;
            }
            else
            {
                s[slow++]=s[fast++];
            }
        }
        //末尾有一个空格
        if(s[slow-1]==' ') s.resize(slow-1);
        //末尾没有空格
        else
        {
            s.resize(slow);
        }
    }
    void swap(char& a,char& b)
    {
        char temp=a;
        a=b;
        b=temp;
    }
    string reverseWords(string s) {
        trim(s);
        for(int i=0,j=s.size()-1;i<j;i++,j--)
        {
            swap(s[i],s[j]);
        }
        int pre=0,cur=0;
        while(cur<=s.size()-1)
        {
            cur++;
            if(s[cur]==' '||cur==s.size())      
            {
                for(int i=pre,j=cur-1;i<j;i++,j--)
                {
                    swap(s[i],s[j]);
                }
                pre=cur+1;
            }

        }
        return s;
    }
};

C++ string resize(int x)，设置string的大小为x，舍去后面多余的字符

左旋转字符串
https://leetcode-cn.com/problems/zuo-xuan-zhuan-zi-fu-chuan-lcof/

class Solution {
public:
    string reverseLeftWords(string s, int n) {
        reverse(s.begin(),s.begin()+n);
        reverse(s.begin()+n,s.end());
        reverse(s.begin(),s.end());
        return s;
    }
};