add: String to Integer (atoi)

Author: hijiangtao

README.md

@@ -12,6 +12,7 @@ This is the solutions collection of my LeetCode submissions, most of them are pr
 |2|[Add Two Numbers](https://leetcode.com/problems/add-two-numbers/) | [JavaScript](./src/add-two-numbers/res.js)|Medium|
 |3|[Longest Substring Without Repeating Characters](https://leetcode.com/problems/longest-substring-without-repeating-characters/) | [JavaScript](./src/longest-substring-without-repeating-characters/res.js) |Medium|
 |7|[Reverse Integer](https://leetcode.com/problems/reverse-integer/) | [JavaScript](./src/reverse-integer/res.js)|Easy|
+|8|[String to Integer (atoi)](https://leetcode.com/problems/string-to-integer-atoi/) | [JavaScript](./src/string-to-integer-atoi/res.js)|Medium|
 |11|[Container With Most Water](https://leetcode.com/problems/container-with-most-water/) | [JavaScript](./src/container-with-most-water/res.js)|Medium|
 |13|[Roman to Integer](https://leetcode.com/problems/roman-to-integer/) | [JavaScript](./src/roman-to-integer/res.js)|Easy|
 |14|[Longest Common Prefix](https://leetcode.com/problems/longest-common-prefix/) | [JavaScript](./src/longest-common-prefix/res.js)|Easy|

src/string-to-integer-atoi/res.js

@@ -0,0 +1,51 @@
+/**
+ * res.js
+ * @authors Joe Jiang (hijiangtao@gmail.com)
+ * @date    2017-04-03 22:44:48
+ *
+ * Problem: Implement atoi to convert a string to an integer.
+ * 
+ * @param {string} str
+ * @return {number}
+ */
+let myAtoi = function(str) {
+   const INT_MAX = 2147483647,
+        INT_MIN = -2147483648,
+        bound = Number.parseInt(INT_MAX/10);
+   let strlen = str.length,
+       signal = 1, // 1 stands for positive number, 0 stands for negative number
+       res = 0;
+   
+   while (str[0] && str[0] === ' ') {
+       str = str.slice(1);
+       strlen -= 1;
+   }
+   
+   if (strlen === 0) {
+       return 0;
+   }
+   
+   if(str[0] === '-') {
+       signal = 0;
+       str = str.slice(1);
+   } else if (str[0] === "+") {
+       str = str.slice(1);
+   }
+   
+   while (str[0] >= '0' && str[0] <= '9') {
+    //   console.log(str[0]);
+       let element = Number.parseInt(str[0]);
+       
+       if ( res>bound || (res===bound && element>7) ) {
+           if(signal) {
+               return INT_MAX;
+           }
+           return INT_MIN;
+       }
+       
+       res = res * 10 + element;
+       str = str.slice(1);
+   }
+   
+   return signal? res:-res;
+};