Put spaces between words starting with capital letters

Last Updated : 20 Jul, 2026

Given a string s containing multiple words concatenated together, where each new word starts with an uppercase letter, insert spaces between the words and convert all characters to lowercase.

Examples:

Input: s = "geeksForGeeks"
Output: "geeks for geeks"
Explanation: The words in the string are "geeks", "For", "Geeks". After inserting spaces before each word and converting all characters to lowercase, the resulting sentence is "geeks for geeks".

Input: s = "You"
Output: "you"
Explanation: The only word in the string is "You". After inserting spaces before each word and converting all characters to lowercase, the resulting sentence is "you".

Single Traversal - O(n) Time and O(n) Space

Traverse the string once and build the result directly. Whenever an uppercase character is found, add a space before it unless it is the first character, then convert it to lowercase.

C++ 
#include <iostream>
#include <vector>
using namespace std;

string amendSentence(string s) {
    vector<string> words;
    string word = "";

    for (int i = 0; i < s.size(); i++) {
        if (i > 0 && s[i] >= 'A' && s[i] <= 'Z') {
            words.push_back(word);
            word = "";
        }

        if (s[i] >= 'A' && s[i] <= 'Z') {
            word += (s[i] - 'A' + 'a');
        } else {
            word += s[i];
        }
    }

    words.push_back(word);

    string res = words[0];

    for (int i = 1; i < words.size(); i++) {
        res += " " + words[i];
    }

    return res;
}

int main() {
    string s = "geeksForGeeks";
    cout << amendSentence(s) << endl;

    s = "You";
    cout << amendSentence(s) << endl;

    return 0;
}
Java 
import java.util.*;

class GFG {
    static String amendSentence(String s) {
        ArrayList<String> words = new ArrayList<>();
        StringBuilder word = new StringBuilder();

        for (int i = 0; i < s.length(); i++) {
            if (i > 0 && s.charAt(i) >= 'A' && s.charAt(i) <= 'Z') {
                words.add(word.toString());
                word = new StringBuilder();
            }

            if (s.charAt(i) >= 'A' && s.charAt(i) <= 'Z') {
                word.append((char)(s.charAt(i) - 'A' + 'a'));
            } else {
                word.append(s.charAt(i));
            }
        }

        words.add(word.toString());

        return String.join(" ", words);
    }

    public static void main(String[] args) {
        String s = "geeksForGeeks";
        System.out.println(amendSentence(s));

        s = "You";
        System.out.println(amendSentence(s));
    }
}
Python 
def amendSentence(s):
    words = []
    word = []

    for i in range(len(s)):
        if i > 0 and 'A' <= s[i] <= 'Z':
            words.append(''.join(word))
            word = []

        if 'A' <= s[i] <= 'Z':
            word.append(chr(ord(s[i]) - ord('A') + ord('a')))
        else:
            word.append(s[i])

    words.append(''.join(word))

    return ' '.join(words)


if __name__ == "__main__":
    s = "geeksForGeeks"
    print(amendSentence(s))

    s = "You"
    print(amendSentence(s))
C# 
using System;
using System.Collections.Generic;
using System.Text;

class GFG {
    static string amendSentence(string s) {
        List<string> words = new List<string>();
        StringBuilder word = new StringBuilder();

        for (int i = 0; i < s.Length; i++) {
            if (i > 0 && s[i] >= 'A' && s[i] <= 'Z') {
                words.Add(word.ToString());
                word = new StringBuilder();
            }

            if (s[i] >= 'A' && s[i] <= 'Z') {
                word.Append((char)(s[i] - 'A' + 'a'));
            } else {
                word.Append(s[i]);
            }
        }

        words.Add(word.ToString());

        return string.Join(" ", words);
    }

    static void Main() {
        string s = "geeksForGeeks";
        Console.WriteLine(amendSentence(s));

        s = "You";
        Console.WriteLine(amendSentence(s));
    }
}
JavaScript 
function amendSentence(s) {
    let words = [];
    let word = "";

    for (let i = 0; i < s.length; i++) {
        if (i > 0 && s[i] >= 'A' && s[i] <= 'Z') {
            words.push(word);
            word = "";
        }

        if (s[i] >= 'A' && s[i] <= 'Z') {
            word += String.fromCharCode(
                s.charCodeAt(i) - 'A'.charCodeAt(0) + 'a'.charCodeAt(0)
            );
        } else {
            word += s[i];
        }
    }

    words.push(word);

    return words.join(" ");
}

// Driver Code
let s = "geeksForGeeks";
console.log(amendSentence(s));

s = "You";
console.log(amendSentence(s));

Output
geeks for geeks
you
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