Update README.md

Author: assassint2017

README.md

@@ -4,7 +4,7 @@
 # leetcode-algorithm
 |total|easy|medium|hard|
 |:---:|:---:|:---:|:---:|
-|264|96|132|36|
+|265|96|133|36|
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 1. [Two Sum](https://github.com/assassint2017/leetcode-algorithm/tree/master/Two%20Sum)
 2. [Add Two Numbers](https://github.com/assassint2017/leetcode-algorithm/tree/master/Add%20Two%20Numbers)
@@ -245,6 +245,7 @@
 421. [Maximum XOR of Two Numbers in an Array](https://github.com/assassint2017/leetcode-algorithm/tree/master/Maximum%20XOR%20of%20Two%20Numbers%20in%20an%20Array)
 429. [N-ary Tree Level Order Traversal](https://github.com/assassint2017/leetcode-algorithm/tree/master/N-ary%20Tree%20Level%20Order%20Traversal)
 437. [Path Sum III](https://github.com/assassint2017/leetcode-algorithm/tree/master/Path%20Sum%20III)
+451. [Sort Characters By Frequency](https://github.com/assassint2017/leetcode-algorithm/tree/master/Sort%20Characters%20By%20Frequency)
 464. [Can I Win](https://github.com/assassint2017/leetcode-algorithm/tree/master/Can%20I%20Win)
 475. [Heaters](https://github.com/assassint2017/leetcode-algorithm/tree/master/Heaters)
 491. [Increasing Subsequences](https://github.com/assassint2017/leetcode-algorithm/tree/master/Increasing%20Subsequences)