Update README.md

Author: fengvyi

README.md

@@ -9,6 +9,7 @@ My C++ solutions of [LeetCode Online Judge](https://leetcode.com/problemset/algo
 |  3  | [Longest Substring Without Repeating Characters](https://leetcode.com/problems/longest-substring-without-repeating-characters/description/) | [C++](https://github.com/fengvyi/LeetCode/blob/master/C%2B%2B/003.%20Longest%20Substring%20Without%20Repeating%20Characters.cpp) | Medium | Hash Table / Two Pointers | [discuss](https://discuss.leetcode.com/topic/101653/8-lines-c-o-n) |
 |  5  | [Longest Palindromic Substring](https://leetcode.com/problems/longest-palindromic-substring/description/) | [C++](https://github.com/fengvyi/LeetCode/blob/master/C%2B%2B/005.%20Longest%20Palindromic%20Substring.cpp) | Medium | String | [discuss](https://discuss.leetcode.com/topic/77099/share-my-ac-c-brute-force-solution-easy-to-understand) |
 |  6  | [ZigZag Conversion](https://leetcode.com/problems/zigzag-conversion/description/) | [C++](https://github.com/fengvyi/LeetCode/blob/master/C%2B%2B/006.%20ZigZag%20Conversion.cpp) | Medium | String | [discuss](https://discuss.leetcode.com/topic/93378/c-13-lines) |
+|  7  | [Reverse Integer](https://leetcode.com/problems/reverse-integer/description/) | [C++](https://github.com/fengvyi/LeetCode/blob/master/C%2B%2B/007.%20Reverse%20Integer.cpp) | Easy | Math | [discuss](https://discuss.leetcode.com/topic/101662/share-my-straightforward-c) |
 |  8  | [String to Integer (atoi)](https://leetcode.com/problems/string-to-integer-atoi/description/) | [C++](https://github.com/fengvyi/LeetCode/blob/master/C%2B%2B/008.%20String%20to%20Integer%20(atoi).cpp) | Medium | String | [discuss](https://discuss.leetcode.com/topic/77861/straight-forward-c-12ms-solution-updated) |
 | 12  | [Integer to Roman](https://leetcode.com/problems/integer-to-roman/description/) | [C++](https://github.com/fengvyi/LeetCode/blob/master/C++/012.%20Integer%20to%20Roman.cpp) | Medium | String | [discuss](https://discuss.leetcode.com/topic/85649/c-the-real-step-by-step-solution) |
 | 13  | [Roman to Integer](https://leetcode.com/problems/roman-to-integer/description/) | [C++](https://github.com/fengvyi/LeetCode/blob/master/C%2B%2B/013.%20Roman%20to%20Integer.cpp) | Easy | String | [discuss](https://discuss.leetcode.com/topic/85643/simple-c-8-lines-o-n-solution) |