Cracking the Coding Interview Q1.4

package chapter1;

/**
* Write a method to replace all spaces in a string with ‘%20’. (Assume string
* has sufficient free space at the end)
*
* @author jd
*
*/
public class Q1_4 {

/**
* 1. Count the number of spaces during the first scan of the string.
* 2.Parse the string again from the end and for each character:
* if a space is encountered, store '%20';
* else store the character as it is in the newly shifted location.
*/
public static void replaceSpaces(char[] str, int length) {
if (str == null)
return;
int spaceCount = 0;
for (int i = 0; i < str.length; i++) {
if (str[i] == ' ')
spaceCount++;
}
int newLength = length + 2 * spaceCount;
for (int i = length - 1, j = newLength - 1; i >= 0 && j >= 0; i--) {
if (str[i] != ' ') {
str[j--] = str[i];
} else {
str[j--] = '0';
str[j--] = '2';
str[j--] = '%';
}

}

}

public static void main(String[] args) {
String str = "abc d e f";
char[] arr = new char[str.length() + 3 * 2 + 1];
for (int i = 0; i < str.length(); i++) {
arr[i] = str.charAt(i);
}
replaceSpaces(arr, str.length());
System.out.println("\"" + new String(arr) + "\"");
}
}

public static void replaceSpaces(char[] str, int length) {
int spaceCount = 0, index, i = 0;
for (i = 0; i < length; i++) {
if (str[i] == ' ') {
spaceCount++;
}
}
index = length + spaceCount * 2;
str[index] = '\0';
for (i = length - 1; i >= 0; i--) {
if (str[i] == ' ') {
str[index - 1] = '0';
str[index - 2] = '2';
str[index - 3] = '%';
index = index - 3;
} else {
str[index - 1] = str[i];
index--;
}
}
}