add SumOfTwoInt

Author: yang-cc

imooc_fengsehng/InputStringToInt.java renamed to imooc_fengsehng/_01_InputStringToInt.java

@@ -7,7 +7,7 @@
 */
 import java.util.Scanner;
 
-public class InputStringToInt
+public class _01_InputStringToInt
 {
 	public static void main(String[] args)
 	{

imooc_fengsehng/CountingBits.java renamed to imooc_fengsehng/_02_CountingBits.java

@@ -6,7 +6,7 @@
  * 来源：慕课网
  * 本文原创发布于慕课网 ，转载请注明出处，谢谢合作！
  */
-public class CountingBits {
+public class _02_CountingBits {
     public static void main(String[] args) {
         int num = 7;
         System.out.println("num:" + num);

imooc_fengsehng/_03_SumOfTwoInt.java

@@ -0,0 +1,43 @@
+/**
+ * Calculate the sum of two integers a and b, but you are not allowed to use the operator + and -.
+ * 作者： fengsehng
+ * 链接：http://www.imooc.com/article/11317
+ * 来源：慕课网
+ * 本文原创发布于慕课网 ，转载请注明出处，谢谢合作！
+ */
+public class _03_SumOfTwoInt {
+    public static void main(String[] args) {
+        int a = 3, b = 10;
+        int sum1 = getSum1(a, b);
+        int sum2 = getSum2(a, b);
+        System.out.println("two integer:" + a + ", " + b);
+        System.out.println("sum1:" + sum1);
+        System.out.println("sum2:" + sum2);
+    }
+//    异或又被称其为“模2加法“
+//    设置变量recipe模拟进位数字，模拟加法的实现过程
+    public static int getSum1(int a, int b){
+        int r = 0, c = 0, recipe = 1;
+        while ((a | b | c) != 0) {
+            if (((a ^ b ^ c) & 1) != 0)
+                r += recipe;
+            recipe <<= 1;
+            c = (a & b | b & c | a & c) & 1;
+            a >>>= 1;
+            b >>>= 1;
+        }
+        return r;
+    }
+
+//    a ^ b,求得结果
+//    a & b，求得进位
+//    相加
+    public static int getSum2(int a, int b){
+        while (b != 0){
+            int c = a & b; //carry
+            a ^= b; //add
+            b = c << 1;
+        }
+        return a;
+    }
+}