# Write a method to replace all spaces in a string with '% 20'

I have a question about a programming problem from the book Cracking The Code Interview by Gayl Laakmann McDowell, 5th Edition.

The problem states: Write a method to replace all spaces in a string with '%20'. Assume string has sufficient space at end of string to hold additional characters, and that you're given a true length of a string. I used the books code, implementing the solution in Java using a character array (given the fact that Java Strings are immutable):

``````public class Test {
public void replaceSpaces(char[] str, int length) {
int spaceCount = 0, newLength = 0, i = 0;

for(i = 0; i < length; i++) {
if (str[i] == ' ')
spaceCount++;
}

newLength = length + (spaceCount * 2);
str[newLength] = '\0';
for(i = length - 1; i >= 0; i--) {
if (str[i] == ' ') {
str[newLength - 1] = '0';
str[newLength - 2] = '2';
str[newLength - 3] = '%';
newLength = newLength - 3;
}
else {
str[newLength - 1] = str[i];
newLength = newLength - 1;
}
}
System.out.println(str);
}

public static void main(String[] args) {
Test tst = new Test();
char[] ch = {'t', 'h', 'e', ' ', 'd', 'o', 'g', ' ', ' ', ' ', ' ', ' ', ' '};
int length = 6;
tst.replaceSpaces(ch, length);
}
}
```
```

The output I am getting from the `replaceSpaces()` call is: the%20do which is cutting of the last character of the original array. I have been scratching my head over this, can anyone explain to me why the algorithm is doing this?

You are passing the length as 6, which is causing this. Pass length as 7 including space. Other wise

``````for(i = length - 1; i >= 0; i--) {
```
```

will not consider last char.