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.) EXAMPLE …

CC150-1.4.java

public class Main {

	/**
	 * @* Runtime & space
   	    * runtime: O(n)
            * space: O(1)  
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Main so = new Main();
		String s="Mr John Smith               ";
		so.replaceSpaces(s.toCharArray(), 13);
	}

	public void replaceSpaces(char[] input, int trueLength){
	
		if(input==null||trueLength==0||input.length==0)
			return;
	
		int count=0;
		//first scan of the array: get the number of the spaces
		for(int i=0;i<trueLength;i++){
			if(input[i]==' ')
				count++;
		}
		//2nd scan: start from the end to replace char[] in space.
		int iLength=trueLength+2*count;
		int p=iLength-1;
		for(int i=trueLength-1;i>=0;i--){
			if(input[i]==' '){
				input[p--]='0';
				input[p--]='2';
				input[p--]='%';
			}else{
				input[p]=input[i];
				p--;
			}
		}
		System.out.println(new String(input));
	}
}