#CC150 #CC150-chap1 1.2 Implement a function void reverse(char* str) in C or C++ which reverses a null-terminated string.

ReverseAString.java

//1.2 Implement a function void reverse(char* str) in C or C++ which reverses a null-terminated string.

public class ReverseAString{

	/** Time: O(n), Space O(n)
	 * Find the middle point of the array, swap each pair of char that is before
	 * and after the middle point with the same distance
	 */
	public static String reverseStr(String str) {
		if (str == null || str.isEmpty()) {
			return null;
		}
		// Turn the string into a char array
		char[] chars = str.toCharArray();
		int len = chars.length;
		int mid = len / 2;// By default, int returns the floor of the division
							// result
		for (int i = 0; i < mid; i++) {
			// Swap the values in position i and in position len-1-i		
				swap(chars, i, len - 1 - i);
		}
		return new String(chars);
	}

	private static void swap(char[] chars, int i, int j) {
		char tmp = chars[i];
		chars[i] = chars[j];
		chars[j] = tmp;
	}

	public static void main(String args[]) {
		String str1 = "abc";
		String str2 = "abcd";
		System.out.println(reverseStr(str1));
		System.out.println(reverseStr(str2));
	}
}