add 007

Author: andavid

Diff for: README.md

@@ -32,7 +32,7 @@
 | #    | Title                                       |
 | :--: | :------------------------------------------ |
 | 344  | [Reverse String][344]                       |
-
+| 7    | [Reverse Integer][007]                      |
 
 **其他**
 
@@ -59,3 +59,4 @@
 [036]: https://github.com/andavid/leetcode-java/blob/master/note/036/README.md
 [048]: https://github.com/andavid/leetcode-java/blob/master/note/048/README.md
 [344]: https://github.com/andavid/leetcode-java/blob/master/note/344/README.md
+[007]: https://github.com/andavid/leetcode-java/blob/master/note/007/README.md

Diff for: note/007/README.md

@@ -0,0 +1,53 @@
+# [Reverse Integer][title]
+
+## Description
+
+Given a 32-bit signed integer, reverse digits of an integer.
+
+**Example 1:**
+
+```
+Input: 123
+Output:  321
+```
+
+**Example 2:**
+
+```
+Input: -123
+Output: -321
+```
+
+**Example 3:**
+
+```
+Input: 120
+Output: 21
+```
+
+**Note:**
+
+Assume we are dealing with an environment which could only hold integers within the 32-bit signed integer range. For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.
+
+## 思路
+使用长整型保存结果。依次模 10 得到最右边一位。
+
+## [完整代码][src]
+
+```java
+class Solution {
+  public int reverse(int x) {
+    long result = 0;
+    for (; x != 0; x /= 10) {
+      result = result * 10 + x % 10;
+    }
+    if (result > Integer.MAX_VALUE || result < Integer.MIN_VALUE) {
+      return 0;
+    }
+    return (int)result;
+  }
+}
+```
+
+[title]: https://leetcode.com/problems/reverse-integer
+[src]: https://github.com/andavid/leetcode-java/blob/master/src/com/andavid/leetcode/_007/Solution.java

Diff for: src/com/andavid/leetcode/_007/Solution.java

@@ -0,0 +1,19 @@
+class Solution {
+  public int reverse(int x) {
+    long result = 0;
+    for (; x != 0; x /= 10) {
+      result = result * 10 + x % 10;
+    }
+    if (result > Integer.MAX_VALUE || result < Integer.MIN_VALUE) {
+      return 0;
+    }
+    return (int)result;
+  }
+
+  public static void main(String[] args) {
+    Solution solution = new Solution();
+    System.out.println(solution.reverse(123));
+    System.out.println(solution.reverse(-123));
+    System.out.println(solution.reverse(120));
+  }
+}