gistfile1.java

class Solution{
  // Space complexity: O(n);
  // Time complexity: O(n);
  public static char[] replaceSpaces(char[] str){
    if(str == null) return null;
    if(str.length == 0 ) return str;
    
    int length = 3 * str.length; // Triple its original size to ensure enough space to hold the result.
    int i = 0; // The index of current character.
    char[] result = new char[length]; // Create a new array to store the result string.

    
    for(char c: str){
      if(c == " ") {
        temp[i++] = "%";
        temp[i++] = "2";
        temp[i++] = "0";
      }
      else{
        temp[i++] = c;
      }
    }
    
    return temp;
  }
}