add question description

README.md

@@ -1 +1,52 @@
 # Broken_Keyboard
+
+##Problem Description
+```
+
+On a broken keyboard, some of the keys are worn out. So when you type some sentences, the characters 
+corresponding to those keys will not appear on screen.
+
+Now given a string that you are supposed to type, and the string that you actually type out, please list those keys 
+which are for sure worn out. 
+输入描述:
+Each input file contains one test case. For each case, the 1st line contains the original string, and the 2nd line contains the typed-out string. Each string contains 
+
+no more than 80 characters which are either English letters [A-Z] (case 
+
+insensitive), digital numbers [0-9], or "_" (representing the space). It is guaranteed that both strings are non-empty.
+
+
+输出描述:
+For each test case, print in one line the keys that are worn out, in the order of being detected. The English letters must be capitalized. 
+
+Each worn out key must be printed once only. It is guaranteed that there is at least one worn out key.
+
+输入例子(input case):
+7_This_is_a_test
+On a broken keyboard, some of the keys are worn out. So when you type some sentences, the characters 
+corresponding to those keys will not appear on screen.
+
+Now given a string that you are supposed to type, and the string that you actually type out, please list those keys 
+which are for sure worn out. 
+输入描述:
+Each input file contains one test case. For each case, the 1st line contains the original string, and the 2nd line contains the typed-out string. Each string contains 
+
+no more than 80 characters which are either English letters [A-Z] (case 
+
+insensitive), digital numbers [0-9], or "_" (representing the space). It is guaranteed that both strings are non-empty.
+
+
+输出描述:
+For each test case, print in one line the keys that are worn out, in the order of being detected. The English letters must be capitalized. 
+
+Each worn out key must be printed once only. It is guaranteed that there is at least one worn out key.
+
+输入例子:
+7_This_is_a_test
+
+_hs_s_a_es
+
+输出例子:
+7TI
+
+```

src/main.java

@@ -2,13 +2,16 @@ public class main {
 
 	public static void main(String[] args) {
 		// TODO Auto-generated method stub
-		System.out.println(func("7_This_is_a_test", "_hs_s_a_es"));
+		System.out.println("the broken keys are:" +func("7_This_is_a_test", "_hs_s_a_es"));
 	}
 
-	/*
-	 * 7_This_is_a_test _hs_s_a_es
+	/* characters typed:
+	 * 7_This_is_a_test
+	 * ---------------
+	 * characters on screen:
+	 * _hs_s_a_es
 	 */
-
+	
 	static public String func(String input, String output) {
 		String missingPart = "";
 		String inputUpcase = input.toUpperCase();