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+
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+##Quiz 1
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+There is a table World
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+
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+ +-----------------+------------+------------+--------------+---------------+
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+ | name | continent | area | population | gdp |
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+ +-----------------+------------+------------+--------------+---------------+
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+ | Afghanistan | Asia | 652230 | 25500100 | 20343000 |
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+ | Albania | Europe | 28748 | 2831741 | 12960000 |
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+ | Algeria | Africa | 2381741 | 37100000 | 188681000 |
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+ | Andorra | Europe | 468 | 78115 | 3712000 |
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+ | Angola | Africa | 1246700 | 20609294 | 100990000 |
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+ +-----------------+------------+------------+--------------+---------------+
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+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)_
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+
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+Write a SQL solution to output big countries' name, population and area.
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+For example, according to the above table, we should output:
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+
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+ +--------------+-------------+--------------+
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+ | name | population | area |
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+ +--------------+-------------+--------------+
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+ | Afghanistan | 25500100 | 652230 |
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+ | Algeria | 37100000 | 2381741 |
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+ +--------------+-------------+--------------+
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+
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+##Quiz 2
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+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)_
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+
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+Table: Customers.
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+
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+ +----+-------+
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+ | Id | Name |
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+ +----+-------+
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+ | 1 | Joe |
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+ | 2 | Henry |
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+ | 3 | Sam |
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+ | 4 | Max |
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+ +----+-------+
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+Table: Orders.
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+
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+ +----+------------+
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+ | Id | CustomerId |
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+ +----+------------+
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+ | 1 | 3 |
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+ | 2 | 1 |
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+ +----+------------+
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+Using the above tables as example, return the following:
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+
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+ +-----------+
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+ | Customers |
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+ +-----------+
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+ | Henry |
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+ | Max |
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+ +-----------+
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+
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+##Quiz 3
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+
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+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.
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+
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+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)_
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+
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+### Test Case 1:
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+ Input: J = "aA", S = "aAAbbbb"
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+ Output: 3
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+### Test Case 2:
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+ Input: J = "z", S = "ZZ"
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+ Output: 0
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+### Note:
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+* S and J will consist of letters and have length at most 50.
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+* The characters in J are distinct.
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+
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+### Example Code (Ruby):
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+ # @param {String} j
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+ # @param {String} s
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+ # @return {Integer}
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+ def num_jewels_in_stones(j, s)
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+ end
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+
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+##Quiz 4
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+
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+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.
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+
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+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)_
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+
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+### Test Case 1:
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+ Input: "UD"
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+ Output: true
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+
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+### Test Case 2:
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+ Input: "LL"
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+ Output: false
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+
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+### Example Code (Ruby):
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+ # @param {String} moves
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+ # @return {Boolean}
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+ def judge_circle(moves)
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+ end
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+
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+
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