cc150-1.4

gistfile1.java

package ch1;

/*
1.4 Write a method to replace all spaces in a string with'%20'. You may assume that
the string has sufficient space at the end of the string to hold the additional
characters, and that you are given the "true" length of the string. (Note: if implementing
in Java, please use a character array so that you can perform this operation
in place.)

* The core condition is that we have sufficient space at the end.
* if we don't care about space, we can just create a new space for new char array.
* In our case, we want to minimize the pace usage, so we start to assign values from the end of the char array
* first, calculate how much space we need according to the number of space
* second, assign new value to the same string from the end, becasue we have many space at the end and we only need 
* this one char array in this case.

 Time Complexity O(n) Space O(1)
 
*/

public class ReplaceSpace {
	
	public static String replace(String arg, int length) {
		char[] cha = arg.toCharArray();
		int countSpace=0;
		int newLength;
		
		for(int i=0; i<length; i++) {
			if(cha[i]==' ') {
				countSpace++;
			}
		}
		
		newLength = length + 2*countSpace;
		int j = length-1;
		for(int i=newLength-1;i>=0;i--){
			if(cha[j] != ' ') {
				cha[i]=cha[j];
			}else {
				cha[i]='0';
				cha[i-1]='2';
				cha[i-2]='%';
				i = i-2;
			}
			j--;		
		}
		arg= new String(cha);
		return arg;
	}

	public static void main(String[] args) {
		String a = "I am so strong                       ";
//		char[] cha = a.toCharArray();
//		a =cha.toString();
		System.out.println(replace(a, 14));
	}

}