cc150.1.4.java

/**
 * 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.)
 * 
 * EXAMPLE
 * Input: "Mr John Smith"
 * Output: "Mr%20Dohn%20Smith"
 * 
 * 
 * @author james
 *
 */
public class ReplaceSpace {
	public static int solution(char[] str, int len) {
		if (str == null || len == 0) {
			return 0;
		}
		
		int count = 0;
		for (int i = 0; i < len; ++i) {
			if (str[i] == ' ') {
				++count;
			}
		}
		
		int newLen = len + count * 2;
		int newTail = newLen -1;
		int oldTail = len -1;

		while(newTail != oldTail) {
			if (str[oldTail] == ' ') {
				str[newTail--] = '0';
				str[newTail--] = '2';
				str[newTail--] = '%';
				--oldTail;
			} else {
				str[newTail--] = str[oldTail--];
			}
		}
		
		return newLen;
	}
}

testReplaceSpace.java

import static org.junit.Assert.*;

import org.junit.Test;


public class TestReplaceSpace {

	@Test
	public void test() {

		int newLen = ReplaceSpace.solution(null, 1);
		assertEquals(newLen, 0);

		newLen = ReplaceSpace.solution(null, 0);
		assertEquals(newLen, 0);

		testSolution("", 0);

		testSolution(" ", 2);

		testSolution("  ", 4);

		testSolution("Hello world!", 2);

		testSolution(" Hello world!", 4);

		testSolution(" Hello world! ", 6);

		testSolution("Hello,world!", 0);
	}
	
	private void testSolution(String s, int result) {
		char[] str = new char[100];

		for(int i = 0; i < s.length(); ++i) {
			str[i] = s.charAt(i);
		}
		System.out.println("old: \"" + s + "\"");

		assertEquals(ReplaceSpace.solution(str, s.length()), s.length() + result);

		System.out.println("new: \"" + new String(str) + "\"");
		
	}

}