CC_1_4

SpaceReplacement.java

// Craking the Coding Interview
// 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"
import java.util.Arrays;
class SpaceReplacement {
	public static char[] replaceSpace(char[] arr, int len) {
		if (arr == null || len <= 0) return arr;
		// calculate space number
		int spaceNum = 0;
		for (int i = 0; i < len; i++) {
			if (arr[i] == ' ') {
				spaceNum++;
			}
		}
		if (spaceNum == 0) return arr;

		// calculate new length
		int newLen = spaceNum*2 + len;

		// move chars back
		int p1 = len-1;
		int p2 = newLen-1;
		while(p2 >= 0) {
			if (arr[p1] == ' ') {
				arr[p2--] = '0';
				arr[p2--] = '2';
				arr[p2--] = '%';
			} else {
				arr[p2--] = arr[p1];
			}
			p1--;
		}
		return arr;
	}
	private static char[] strToArr(String s) {
		if (s == null) return null;
		char[] arr = new char[s.replaceAll(" ", "%20").length()];
		for(int i = 0; i < s.length(); i++) {
			arr[i] = s.charAt(i);
		}
		return arr;
	}
	public static void main(String[] args) {
		assert Arrays.equals(replaceSpace(strToArr(""), 0), "".toCharArray());
		assert Arrays.equals(replaceSpace(strToArr(" "), 1), "%20".toCharArray());
		assert Arrays.equals(replaceSpace(null, 2), null);
		assert Arrays.equals(replaceSpace(strToArr("  "), 2), "%20%20".toCharArray());
		assert Arrays.equals(replaceSpace(strToArr(" %20"), 4), "%20%20".toCharArray());
		assert Arrays.equals(replaceSpace(strToArr("%20 "), 4), "%20%20".toCharArray());
		assert Arrays.equals(replaceSpace(strToArr("a b c"), 5), "a%20b%20c".toCharArray());

		System.out.println("Tests Passed\n");
	}

}