add leetcode solution

Author: Zhanganjin0520

README.md

@@ -75,7 +75,8 @@
 |647|[Palindromic Substrings](https://leetcode.com/problems/palindromic-substrings/) | |Medium|
 |643|[Maximum Average Subarray I](https://leetcode.com/problems/maximum-average-subarray-i/description/) | |Easy|
 |628|[Maximum Product of Three Numbers](https://leetcode.com/problems/maximum-product-of-three-numbers/) | |Easy|
-|627|[Swap Salary](https://leetcode.com/problems/swap-salary/) | [Mysql](./algorithm/swapSalary/Solution.java) | |Easy|
+|627|[Swap Salary](https://leetcode.com/problems/swap-salary/) | [Mysql](./algorithm/swapSalary/Solution.java) | |Medium|
+|626|[Exchange Seats](https://leetcode.com/problems/exchange-seats/) | [Mysql](./algorithm/swapSalary/Solution.java) | |Easy|
 |623|[Add One Row to Tree](https://leetcode.com/problems/add-one-row-to-tree/) | |Medium|
 |620|[Not Boring Movies](https://leetcode.com/problems/not-boring-movies/)| [Mysql](./algorithms/notBoringMovies/Solution.sql) |Easy|
 |617|[Merge Two Binary Trees](https://leetcode.com/problems/merge-two-binary-trees/)| [Java](./algorithms/mergeTwoBinaryTrees/Solution.java)
@@ -193,6 +194,7 @@
 |268|[Missing Number](https://leetcode.com/problems/missing-number/)| |Medium|
 |264|[Ugly Number II](https://leetcode.com/problems/ugly-number-ii/)| |Medium|
 |263|[Ugly Number](https://leetcode.com/problems/ugly-number/)| |Easy|
+|262|[Trips and Users](https://leetcode.com/problems/trips-and-users/)| [Mysql](./algorithms/tripsAndUsers/Solution.sql) |Hard|
 |260|[Single Number III](https://leetcode.com/problems/single-number-iii/)| |Medium|
 |258|[Add Digits](https://leetcode.com/problems/add-digits/)| |Easy|
 |257|[Binary Tree Paths](https://leetcode.com/problems/binary-tree-paths/)| |Easy|
@@ -233,7 +235,7 @@
 |208|[Implement Trie (Prefix Tree)](https://leetcode.com/problems/implement-trie-prefix-tree/)| |Medium|
 |207|[Course Schedule](https://leetcode.com/problems/course-schedule/)| |Medium|
 |206|[Reverse Linked List](https://leetcode.com/problems/reverse-linked-list/)| [java](./algorithms/reverseLinkedList/Solution.java), [js](./algorithms/reverseLinkedList/reverseLinkedList.js) |Easy|
-|205|[Isomorphic Strings](https://leetcode.com/problems/isomorphic-strings/)| |Easy|
+|205|[Isomorphic Strings](https://leetcode.com/problems/isomorphic-strings/)| [java](./algorithms/ismorphicStrings/Solution.java) |Easy|
 |204|[Count Primes](https://leetcode.com/problems/count-primes/)| |Easy|
 |203|[Remove Linked List Elements](https://leetcode.com/problems/remove-linked-list-elements/)| [js](./algorithms/removeLinkedListElements/removeLinkedListElements.js),[java](./algorithms/removeLinkedListElements/Solution.java) |Easy|
 |202|[Happy Number](https://leetcode.com/problems/happy-number/)| |Easy|

algorithms/exchangeSeats/Solution.sql

@@ -0,0 +1,16 @@
+-- Write your MySQL query statement below
+-- 交换 Id 确实比较巧妙
+SELECT
+    (CASE
+        WHEN MOD(id, 2) != 0 AND counts != id THEN id + 1
+        WHEN MOD(id, 2) != 0 AND counts = id THEN id
+        ELSE id - 1
+    END) AS id,
+    student
+FROM
+    seat,
+    (SELECT
+        COUNT(*) AS counts
+    FROM
+        seat) AS seat_counts
+ORDER BY id ASC;

algorithms/ismorphicStrings/Solution.java

@@ -0,0 +1,16 @@
+class Solution {
+    public boolean isIsomorphic(String s, String t) {
+        Map<Character, Character> s2t = new HashMap<Character, Character>();
+        Map<Character, Character> t2s = new HashMap<Character, Character>();
+        int len = s.length();
+        for (int i = 0; i < len; ++i) {
+            char x = s.charAt(i), y = t.charAt(i);
+            if ((s2t.containsKey(x) && s2t.get(x) != y) || (t2s.containsKey(y) && t2s.get(y) != x)) {
+                return false;
+            }
+            s2t.put(x, y);
+            t2s.put(y, x);
+        }
+        return true;
+    }
+}

algorithms/tripsAndUsers/Solution.sql

@@ -0,0 +1,15 @@
+-- # Write your MySQL query statement below
+SELECT T.request_at AS `Day`, 
+	ROUND(
+			SUM(
+				IF(T.STATUS = 'completed',0,1)
+			)
+			/ 
+			COUNT(T.STATUS),
+			2
+	) AS `Cancellation Rate`
+FROM Trips AS T
+JOIN Users AS U1 ON (T.client_id = U1.users_id AND U1.banned ='No')
+JOIN Users AS U2 ON (T.driver_id = U2.users_id AND U2.banned ='No')
+WHERE T.request_at BETWEEN '2013-10-01' AND '2013-10-03'
+GROUP BY T.request_at