[Function add]

1, Add leetcode solution.

Author: Seanforfun

README.md

@@ -333,6 +333,8 @@
 
 [185. Department Top Three Salaries](https://github.com/Seanforfun/Algorithm-and-Leetcode/blob/master/leetcode/185.%20Department%20Top%20Three%20Salaries.md)
 
+[187. Repeated DNA Sequences](https://github.com/Seanforfun/Algorithm-and-Leetcode/blob/master/leetcode/187.%20Repeated%20DNA%20Sequences.md)
+
 ## Algorithm(4th_Edition)
 Reading notes of book Algorithm(4th Algorithm),ISBN: 9787115293800.
 All java realization codes are placed in different packages.

leetcode/187. Repeated DNA Sequences.md

@@ -55,4 +55,27 @@ class Solution {
         return new ArrayList<String>(repeat);
     }
 }
+```
+
+### 二刷
+1. 最开始没有想到用两个Set,于是用了Map来记录出现的序列。
+```Java
+class Solution {
+    public List<String> findRepeatedDnaSequences(String s) {
+        List<String> result = new LinkedList<>();
+        Map<String, Integer> map = new HashMap<>();
+        if(s == null || s.length() < 10) return result;
+        int len = s.length();
+        for(int i = 0; i <= len - 10; i++){
+            String sub = s.substring(i, i + 10);
+            if(!map.containsKey(sub)){
+                map.put(sub, 1);
+            }else if(map.get(sub) == 1){
+                result.add(sub);
+                map.put(sub, map.get(sub) + 1);
+            }else continue;
+        }
+        return result;
+    }
+}
 ```