Reverse Words in a String in C++

C++Server Side ProgrammingProgramming

Suppose we have a string with few words. We have to reverse the word positions in the string. So if the string is like “The quick brown fox jumps over a lazy dog”

To solve this, we will follow these steps −

  • Define a function getString(), this will take s as input, this will work as −

  • i := 0, j := size of s – 1

  • while s[i] = ‘ ’ and i < size of s, increase i by 1

  • while j >= 0 and s[j] = ‘ ’, decrease j by 1

  • ret := empty string

  • for i <= j, increase i by 1

    • if size of ret is non-zero and the last element of ret is ‘ ’ and s[i] is ‘ ’, then go for the next iteration

    • ret := ret + s[i]

  • Define another method called reverseWords(), this will take s as input

  • j := 0

  • for I in range 0 to the size of s – 1, in each step set i := j

    • if s[i] is blank, then j := i + 1

    • otherwise

      • while j + 1 < size of s and s[j + 1] is not space, then increase j by 1

      • x := i and y := j

      • while x < y

        • exchange s[x] and s[y], increase x by 1 and decease y by 1

      • increase j by 1

  • From the main method, do the following −

  • reverse the string s

  • reverseWords(s)

  • return getString(s)

Example (C++)

Let us see the following implementation to get a better understanding −

 Live Demo

#include <bits/stdc++.h>
using namespace std;
class Solution {
public:
   string reverseWords(string s) {
      reverse(s.begin(), s.end());
      reverseWordss(s);
      return getString(s);
   }
   string getString(string s){
      int i = 0;
      int j = s.size() - 1;
      while(s[i] == ' ' && i < s.size()) i++;
      while(j >= 0 && s[j] == ' ') j--;
      string ret = "";
      for(;i <= j; i++){
         if(ret.size() && ret.back() == ' ' && s[i] == ' ')continue;
         ret += s[i];
      }
      return ret;
   }
   void reverseWordss(string& s){
      int j = 0;
      for(int i = 0; i < s.size() ;i = j){
         if(s[i] == ' '){
            j = i + 1;
         }
         else{
            while(j + 1 < s.size() && s[j + 1] != ' ') j++;
            int x = i;
            int y = j;
            while(x < y){
               swap(s[x], s[y]);
               x++;
               y--;
            }
            j++;
         }
      }  
   }
};
main(){
   Solution ob;
   cout << (ob.reverseWords("The quick brown fox jumps over a lazy dog"));
}

Input

"The quick brown fox jumps over a lazy dog"

Output

"dog lazy a over jumps fox brown quick The"
raja
Published on 31-Mar-2020 08:34:52
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