add: ZigZag Conversion

Author: hijiangtao

README.md

@@ -11,6 +11,7 @@ This is the solutions collection of my LeetCode submissions, most of them are pr
 |1|[Two Sum](https://leetcode.com/problems/two-sum/) | [JavaScript](./src/two-sum/res.js)|Easy|
 |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|
+|6|[ZigZag Conversion](https://leetcode.com/problems/zigzag-conversion/) | [JavaScript](./src/zigzag-conversion/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|

src/zigzag-conversion/res.js

@@ -0,0 +1,49 @@
+/**
+ * res.js
+ * @authors Joe Jiang (hijiangtao@gmail.com)
+ * @date    2017-05-10 16:32:48
+ * 
+ * Definition of Zigzag: https://en.wikipedia.org/wiki/Zigzag
+ * 
+ * @param {string} s
+ * @param {number} numRows
+ * @return {string}
+ */
+let convert = function(s, numRows) {
+    if (numRows < 2) {
+        return s;
+    }
+    
+    // change string to array
+    let sarray = s.split(''),
+        len = s.length,
+        res = [],
+        index = 0,
+        order = 1; // 显示数组遍历顺序是自上而下还是自下而上
+        
+    for (let i=0; i<numRows; i++) { // 初始化空数组元素
+        res.push([]);
+    }
+    while (index<len) {
+        for (let i=0; i<numRows-1; i++) {
+            if (index>=len) {
+                break;
+            }
+            if (order === 1) { // 根据遍历顺序确定存放的数组元素下标
+                res[i].push(sarray[index]);    
+            } else {
+                res[numRows-1-i].push(sarray[index]);
+            }
+            
+            index++;
+        }
+        order = -order;
+    }
+    
+    res[0] = res[0].join('');
+    for (let i=1; i<numRows; i++) { // 合并数组至字符串
+        res[0] += res[i].join('');
+    }
+    
+    return res[0];
+};