Program to reverse words in a given string in C++
Given a sentence in the form of string str, the task is to reverse each word of the given sentence in C++.
Examples:
Input: str = “the sky is blue”
Output: blue is sky the
Input: str = “I love programming”
Output: programming love I
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Method 1: Using STL functions
- Reverse the given string str using STL function reverse().
- Iterate the reversed string and whenever a space is found reverse the word before that space using the STL function reverse().
Below is the implementation of the above approach:
CPP
// C++ program for the above approach#include <bits/stdc++.h>using namespace std;// Function to reverse the given stringstring reverseString(string str){ // Reverse str using inbuilt function reverse(str.begin(), str.end()); // Add space at the end so that the // last word is also reversed str.insert(str.end(), ' '); int n = str.length(); int j = 0; // Find spaces and reverse all words // before that for (int i = 0; i < n; i++) { // If a space is encountered if (str[i] == ' ') { reverse(str.begin() + j, str.begin() + i); // Update the starting index // for next word to reverse j = i + 1; } } // Remove spaces from the end of the // word that we appended str.pop_back(); // Return the reversed string return str;}// Driver codeint main(){ string str = "I like this code"; // Function call string rev = reverseString(str); // Print the reversed string cout << rev; return 0;} |
Output:
code this like I
Method 2: Without using the inbuilt function: We can create the reverse() function which is used to reverse the given string. Below are the steps:
- Initially reverse each word of the given string str.
- Now reverse the whole string to get the resultant string in desired order.
Below is the implementation of the above approach:
CPP
// C++ program for the above approach#include <bits/stdc++.h>using namespace std;// Function used to reverse a string// from index l to rvoid reversed(string& s, int l, int r){ while (l < r) { // Swap characters at l and r swap(s[l], s[r]); l++; r--; }}// Function to reverse the given stringstring reverseString(string str){ // Add space at the end so that the // last word is also reversed str.insert(str.end(), ' '); int n = str.length(); int j = 0; // Find spaces and reverse all words // before that for (int i = 0; i < n; i++) { // If a space is encountered if (str[i] == ' ') { // Function call to our custom // reverse function() reversed(str, j, i - 1); // Update the starting index // for next word to reverse j = i + 1; } } // Remove spaces from the end of the // word that we appended str.pop_back(); // Reverse the whole string reversed(str, 0, str.length() - 1); // Return the reversed string return str;}// Driver codeint main(){ string str = "I like this code"; // Function call string rev = reverseString(str); // Print the reversed string cout << rev; return 0;} |
Output:
code this like I
Time Complexity: O(N)
Auxiliary Space: O(1)
