feat: add 008

Author: Blankj

README.md

@@ -8,6 +8,7 @@
 |:------------- |:------------- |:------------- |
 |1|[Two Sum][001]|Array, Hash Table|
 |7|[Reverse Integer][007]|Math|
+|8|[String to Integer (atoi)][008]|Math, String|
 
 
 ## Medium
@@ -30,3 +31,4 @@
 [note]: https://github.com/Blankj/awesome-java-leetcode/tree/master/note
 [001]: https://github.com/Blankj/awesome-java-leetcode/blob/master/note/001/README.md
 [007]: https://github.com/Blankj/awesome-java-leetcode/blob/master/note/007/README.md
+[008]: https://github.com/Blankj/awesome-java-leetcode/blob/master/note/008/README.md

note/001/README.md

@@ -1,4 +1,4 @@
-# Two Sum
+# [Two Sum](https://leetcode.com/problems/two-sum/)
 
 ## Description
 
@@ -15,7 +15,7 @@ Because nums[0] + nums[1] = 2 + 7 = 9,
 return [0, 1].
 ```
 
-**Tag：** Array, Hash Table
+**Tags：** Array, Hash Table
 
 
 ## 思路0

note/007/README.md

@@ -1,4 +1,4 @@
-# Reverse Integer
+# [Reverse Integer](https://leetcode.com/problems/reverse-integer/)
 
 ## Description
 
@@ -24,7 +24,7 @@ For the purpose of this problem, assume that your function returns 0 when the re
 
 The input is assumed to be a 32-bit signed integer. Your function should **return 0 when the reversed integer overflows**.
 
-**Tag：** Math
+**Tags：** Math
 
 
 ## 思路

note/008/README.md

@@ -0,0 +1,50 @@
+# [String to Integer (atoi)](https://leetcode.com/problems/string-to-integer-atoi/)
+
+## Description
+
+Implement atoi to convert a string to an integer.
+
+**Hint:** Carefully consider all possible input cases. If you want a challenge, please do not see below and ask yourself what are the possible input cases.
+
+**Notes:** It is intended for this problem to be specified vaguely (ie, no given input specs). You are responsible to gather all the input requirements up front.
+
+**Spoilers：**
+
+**Requirements for atoi:**
+
+The function first discards as many whitespace characters as necessary until the first non-whitespace character is found. Then, starting from this character, takes an optional initial plus or minus sign followed by as many numerical digits as possible, and interprets them as a numerical value.
+
+The string can contain additional characters after those that form the integral number, which are ignored and have no effect on the behavior of this function.
+
+If the first sequence of non-whitespace characters in str is not a valid integral number, or if no such sequence exists because either str is empty or it contains only whitespace characters, no conversion is performed.
+
+If no valid conversion could be performed, a zero value is returned. If the correct value is out of the range of representable values, INT_MAX (2147483647) or INT_MIN (-2147483648) is returned.
+
+**Tags:** Math, String
+
+
+## 思路
+
+题目大意就是把一个字符串转为整型，但要注意所给的要求，先去除最前面的空格，然后判断正负数，注意正数可能包含`+`，如果之后存在非数字或全为空则返回`0`，而如果合法的值超过int表示的最大范围，则根据正负号返回`INT_MAX`或`INT_MIN`。
+
+``` java
+public class Solution {
+    public int myAtoi(String str) {
+        int i = 0, ans = 0, sign = 1, len = str.length();
+        while (i < len && str.charAt(i) == ' ') ++i;
+        if (i < len && (str.charAt(i) == '-' || str.charAt(i) == '+')) {
+            sign = str.charAt(i++) == '+' ? 1 : -1;
+        }
+        for (; i < len; ++i) {
+            int tmp = str.charAt(i) - '0';
+            if (tmp < 0 || tmp > 9)
+                break;
+            if (ans > Integer.MAX_VALUE / 10 || ans == Integer.MAX_VALUE / 10 && Integer.MAX_VALUE % 10 < tmp)
+                return sign == 1 ? Integer.MAX_VALUE : Integer.MIN_VALUE;
+            else
+                ans = ans * 10 + tmp;
+        }
+        return sign * ans;
+    }
+}
+```

project/LeetCode/leetcode/src/main/java/com/blankj/easy/_001/_001.java renamed to project/LeetCode/leetcode/src/main/java/com/blankj/easy/_001/Solution.java

@@ -7,22 +7,12 @@
  * <pre>
  *     author: Blankj
  *     blog  : http://blankj.com
- *     time  : 2017/04/19
+ *     time  : 2017/04/21
  *     desc  :
  * </pre>
  */
 
-public class _001 {
-
-    public static void main(String[] args) {
-        Solution solution = new Solution();
-        int[] nums = new int[]{2, 7, 11, 15};
-        int target = 9;
-        System.out.println(Arrays.toString(solution.twoSum(nums, target)));
-    }
-}
-
-class Solution {
+public class Solution {
 //    public int[] twoSum(int[] nums, int target) {
 //        int st = 0, end = nums.length;
 //        for (int i = 0; i < end; ++i) {
@@ -46,4 +36,11 @@ public int[] twoSum(int[] nums, int target) {
         }
         return null;
     }
-}
+
+    public static void main(String[] args) {
+        Solution solution = new Solution();
+        int[] nums = new int[]{2, 7, 11, 15};
+        int target = 9;
+        System.out.println(Arrays.toString(solution.twoSum(nums, target)));
+    }
+}

project/LeetCode/leetcode/src/main/java/com/blankj/easy/_007/_007.java renamed to project/LeetCode/leetcode/src/main/java/com/blankj/easy/_007/Solution.java

@@ -1,7 +1,5 @@
 package com.blankj.easy._007;
 
-import java.util.Arrays;
-
 /**
  * <pre>
  *     author: Blankj
@@ -11,21 +9,19 @@
  * </pre>
  */
 
-public class _007 {
+public class Solution {
+    public int reverse(int x) {
+        long res = 0;
+        for (; x != 0; x /= 10)
+            res = res * 10 + x % 10;
+        return res > Integer.MAX_VALUE || res < Integer.MIN_VALUE ? 0 : (int) res;
+    }
+
     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(100));
         System.out.println(solution.reverse(1000000003));
     }
-}
-
-class Solution {
-    public int reverse(int x) {
-        long res = 0;
-        for (; x != 0; x /= 10)
-            res = res * 10 + x % 10;
-        return res > Integer.MAX_VALUE || res < Integer.MIN_VALUE ? 0 : (int) res;
-    }
 }

project/LeetCode/leetcode/src/main/java/com/blankj/easy/_008/Solution.java

@@ -0,0 +1,40 @@
+package com.blankj.easy._008;
+
+/**
+ * <pre>
+ *     author: Blankj
+ *     blog  : http://blankj.com
+ *     time  : 2017/04/21
+ *     desc  :
+ * </pre>
+ */
+
+public class Solution {
+    public int myAtoi(String str) {
+        int i = 0, ans = 0, sign = 1, len = str.length();
+        while (i < len && str.charAt(i) == ' ') ++i;
+        if (i < len && (str.charAt(i) == '-' || str.charAt(i) == '+')) {
+            sign = str.charAt(i++) == '+' ? 1 : -1;
+        }
+        for (; i < len; ++i) {
+            int tmp = str.charAt(i) - '0';
+            if (tmp < 0 || tmp > 9)
+                break;
+            if (ans > Integer.MAX_VALUE / 10 || ans == Integer.MAX_VALUE / 10 && Integer.MAX_VALUE % 10 < tmp)
+                return sign == 1 ? Integer.MAX_VALUE : Integer.MIN_VALUE;
+            else
+                ans = ans * 10 + tmp;
+        }
+        return sign * ans;
+    }
+
+    public static void main(String[] args) {
+        Solution solution = new Solution();
+        System.out.println(solution.myAtoi("   +1"));
+        System.out.println(solution.myAtoi("   -1"));
+        System.out.println(solution.myAtoi(""));
+        System.out.println(solution.myAtoi("a1"));
+        System.out.println(solution.myAtoi("100000000000000000000"));
+        System.out.println(solution.myAtoi("-100000000000000000000"));
+    }
+}