Replace Spaces. Input "Mr John Smith " Output "Mr%20John%Smith". CC150 - Arrays and Strings

ReplaceSpaces.java

package CC150.ArraysAndString;

/**
 * 1. Calculate spaces count first, then we know new char[] length 
 * 2. To prevent overlap, start replace from end to head
 *
 * true length < str.length because of input may end with many spaces.
 * length = str.length - end spaces
 * 
 * book use newLength - 1, then newLength--, I use step here.
 */
public class ReplaceSpaces {

	public static void main(String args[]) {
		System.out.println(replaceSpaces("Mr John Smith dsadsa            ".toCharArray(), 20));
	}
	
	public static String replaceSpaces(char[] str, int length) {
		int spaceCount = 0;
		for (int i=0 ; i< length; i++) {
			if (str[i] == ' ') {
				spaceCount++;
			}
		}
		
		int newLength = length + 2 * spaceCount;
		
		str[newLength-1] = '\0'; // always forget here
		int step = 2;
		for(int i=length-1; i>=0 ; i--) {
			if(str[i] != ' ') {
				str[newLength-step] = str[i];
				step++;
			} else {
				str[newLength-step] = '0';
				str[newLength-step-1] = '2';
				str[newLength-step-2] = '%';
				step = step + 3;
			}
		}
		return new String(str);
	}
}