目录

1--反转字符串

2--反转字符串II

3--反转字符串中的单词

4--KMP算法

5--重复的子字符串

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1--反转字符串

主要思路：

        双指针算法，交换两个指针的字符；

#include <iostream>
#include <vector>class Solution {
public:void reverseString(std::vector<char>& s) {if(s.size() == 0) return;int l = 0, r = s.size() - 1;while(l < r){std::swap(s[l], s[r]);l++;r--;}}
};int main(int argc, char* argv[]){// s = ["h","e","l","l","o"]std::vector<char> s = {'h', 'e', 'l', 'l', 'o'};Solution S1;S1.reverseString(s);for(auto c : s) std::cout << c << " ";std::cout << std::endl;return 0;
}

2--反转字符串II

主要思路：

        以 2k 个字符为一组进行遍历；

#include <iostream>
#include <string>
#include <algorithm>class Solution {
public:std::string reverseStr(std::string s, int k) {for(int i = 0; i < s.length(); i += 2*k){if(i + k <= s.length()) {std::reverse(s.begin() + i, s.begin() + i + k);}else{std::reverse(s.begin() + i, s.end());}           }return s;}
};int main(int argc, char* argv[]){// s = "abcdefg", k = 2std::string test = "abcdefg";int k = 2;Solution S1;std::string res = S1.reverseStr(test, k);std::cout << res << std::endl;return 0;
}

3--反转字符串中的单词

主要思路1：

        遍历提取每一个有效的单词，存储在一个栈中，最后遍历栈连接字符串即可；空间复杂度为O(N)；

#include <iostream>     
#include <stack>         
#include <string>       class Solution {
public:std::string reverseWords(std::string s) {std::stack<std::string> stk;std::string tmp = "";for(int i = 0; i < s.length(); i++){if(s[i] == ' ' && tmp == "") continue; // 单词前的空格else if(s[i] == ' ' && tmp != ""){ // 单词间的空格stk.push(tmp);tmp = "";}else{tmp += s[i];}}stk.push(tmp); //最后一个有效单词std::string res;while(!stk.empty()){if(res.length() == 0) res += stk.top();else{res += " ";res += stk.top();}stk.pop();}return res;}
};int main (int argc, char *argv[]){std::string test = "the sky is blue";Solution S1;std::string res = S1.reverseWords(test);std::cout << res << std::endl;return 0;
}

主要思路2:

        不使用辅助空间，要求空间复杂度为O(1)；首先使用快慢指针剔除多余的空格，接着反转所有字符，最后对单词的字符进行再次反转；

#include <iostream>             
#include <string>       
#include <algorithm>class Solution {
public:std::string reverseWords(std::string s) {//去除多余的空格（参考移除数组的元素，使用快慢指针）removeExtraSpace(s);//反转所有字符std::reverse(s.begin(), s.end());//按单词再次反转int start = 0;for(int i = 0; i < s.length(); i++){// 遇到单词间的空格 if(s[i] == ' ') {std::reverse(s.begin()+start, s.begin()+i);start = i + 1;}}// 反转最后一个单词std::reverse(s.begin()+start, s.end());return s;}void removeExtraSpace(std::string &s){int slow = 0;for(int fast = 0; fast < s.length(); fast++){if(s[fast] == ' ') continue;if(slow != 0){ // 单词间的空格s[slow] = ' ';slow++;}while(fast < s.length() && s[fast] != ' '){ //将非空格字符覆盖到slow的位置s[slow] = s[fast];slow++;fast++;}}s.resize(slow);}
};int main (int argc, char *argv[]){std::string test = "the sky is blue";Solution S1;std::string res = S1.reverseWords(test);std::cout << res << std::endl;return 0;
}

4--KMP算法

数据结构笔记--KMP算法的实现

5--重复的子字符串

主要思路：

#include <iostream>
#include <string>
#include <algorithm>class Solution {
public:bool repeatedSubstringPattern(std::string s) {std::string ss = s + s;ss = ss.substr(1, ss.size() - 2);if(ss.find(s) != -1) return true;else return false;}
};int main(int argc, char* argv[]){// s = "abab"std::string test = "abab";Solution S1;bool res = S1.repeatedSubstringPattern(test);if(res) std::cout << "true" << std::endl;else std::cout << "false" << std::endl;return 0;
}