[Interview]: URLify

[Interview] URLify:

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Question:

URLify:

Write a method to replace all spaces in a string with

‘%20’, you may assume that the string has sufficient space at the

end to hold the additional characters.

Example 

input: 'mr john smith ' 

output: 'mr%20john%20smith'

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Idea 1: 
Start from the back and start replacing until the character is not ' ', and replace the characters in reverse order.

Solution 1：

public class Solution{
 public String replace(char[] str) {
  boolean flag = false;
  StringBuffer sb = new StringBuffer();
  for (int i = str.length - 1; i >= 0; i--) {
   if (str[i] != ' ')
    flag = true;

   if (flag == true) {

    if (str[i] == ' ') {
     sb.append('0');
     sb.append('2');
     sb.append('%');

    } else {
     sb.append(str[i]);
    }

   }
  }
  return sb.reverse().toString();
 }

}

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Video Explanation: