add interview quiz

Quiz-for-interview.md

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+
+##Quiz 1
+There is a table World
+
+    +-----------------+------------+------------+--------------+---------------+
+    | name            | continent  | area       | population   | gdp           |
+    +-----------------+------------+------------+--------------+---------------+
+    | Afghanistan     | Asia       | 652230     | 25500100     | 20343000      |
+    | Albania         | Europe     | 28748      | 2831741      | 12960000      |
+    | Algeria         | Africa     | 2381741    | 37100000     | 188681000     |
+    | Andorra         | Europe     | 468        | 78115        | 3712000       |
+    | Angola          | Africa     | 1246700    | 20609294     | 100990000     |
+    +-----------------+------------+------------+--------------+---------------+
+A country is big if it has an area of bigger than 3 million square km or a population of more than 25 million. _(595. Big Countries)_
+
+Write a SQL solution to output big countries' name, population and area.
+For example, according to the above table, we should output:
+
+    +--------------+-------------+--------------+
+    | name         | population  | area         |
+    +--------------+-------------+--------------+
+    | Afghanistan  | 25500100    | 652230       |
+    | Algeria      | 37100000    | 2381741      |
+    +--------------+-------------+--------------+
+    
+##Quiz 2
+Suppose that a website contains two tables, the Customers table and the Orders table. Write a SQL query to find all customers who never order anything. _(183. Customers Who Never Order)_
+
+Table: Customers.
+
+    +----+-------+
+    | Id | Name  |
+    +----+-------+
+    | 1  | Joe   |
+    | 2  | Henry |
+    | 3  | Sam   |
+    | 4  | Max   |
+    +----+-------+
+Table: Orders.
+
+    +----+------------+
+    | Id | CustomerId |
+    +----+------------+
+    | 1  | 3          |
+    | 2  | 1          |
+    +----+------------+
+Using the above tables as example, return the following:
+
+    +-----------+
+    | Customers |
+    +-----------+
+    | Henry     |
+    | Max       |
+    +-----------+
+    
+##Quiz 3
+
+You're given strings J representing the types of stones that are jewels, and S representing the stones you have.  Each character in S is a type of stone you have.  You want to know how many of the stones you have are also jewels.
+
+The letters in J are guaranteed distinct, and all characters in J and S are letters. Letters are case sensitive, so "a" is considered a different type of stone from "A". _(771. Jewels and Stones)_
+
+### Test Case 1:
+    Input: J = "aA", S = "aAAbbbb"
+    Output: 3
+### Test Case 2:
+    Input: J = "z", S = "ZZ"
+    Output: 0
+### Note:
+* S and J will consist of letters and have length at most 50.
+* The characters in J are distinct.
+
+### Example Code (Ruby):
+    # @param {String} j
+    # @param {String} s
+    # @return {Integer}
+    def num_jewels_in_stones(j, s)
+    end  
+    
+##Quiz 4
+
+Initially, there is a Robot at position (0, 0). Given a sequence of its moves, judge if this robot makes a circle, which means it moves back to the original place.
+
+The move sequence is represented by a string. And each move is represent by a character. The valid robot moves are R (Right), L (Left), U (Up) and D (down). The output should be true or false representing whether the robot makes a circle. _(657. Judge Route Circle)_
+
+### Test Case 1:
+    Input: "UD"
+    Output: true
+
+### Test Case 2:
+    Input: "LL"
+    Output: false
+    
+### Example Code (Ruby):
+    # @param {String} moves
+    # @return {Boolean}
+    def judge_circle(moves)
+    end
+
+