zigzag conversion

Author: fishercoder1534

EASY/src/easy/ZigZagConversion.java

@@ -0,0 +1,30 @@
+package easy;
+
+public class ZigZagConversion {
+
+    public String convert(String s, int numRows) {
+        StringBuilder[] sb = new StringBuilder[numRows];
+        char[] c= s.toCharArray();
+        int len = s.length();
+        for(int i = 0; i < numRows; i++){
+            sb[i] = new StringBuilder();//this is an important step to initialize it
+        }
+        int i = 0;
+        while(i < len){
+            for(int index = 0; index < numRows && i < len; index++){
+                sb[index].append(c[i++]);// vertically down
+            }
+            
+            for(int index = numRows - 2; index >= 1 && i < len; index--){/**Why it should start from numRows - 2? Think of the example when numRows = 3
+            the starting point of obliquely going up is 1, which is numRows-2.*/
+                sb[index].append(c[i++]);// obliquely up
+            }
+        }
+        
+        for(i = 1; i < numRows; i++){
+            sb[0].append(sb[i]);
+        }
+        return sb[0].toString();
+    }
+
+}

README.md

@@ -71,6 +71,7 @@
 |9|[Palindrome Number](https://leetcode.com/problems/palindrome-number/)|[Solution](../../blob/master/EASY/src/easy/PalindromeNumber.java)| O(logn)/(n) | O(1) | Easy
 |8|[String to Integer (atoi)](https://leetcode.com/problems/string-to-integer-atoi/)|[Solution](../../blob/master/EASY/src/easy/StringToInteger.java)| O(n) | O(1) | Easy
 |7|[Reverse Integer](https://leetcode.com/problems/reverse-integer/)|[Solution](../../blob/master/EASY/src/easy/ReverseInteger.java) | O(1) | O(1) | Easy | 
+|6|[ZigZag Conversion](https://leetcode.com/problems/zigzag-conversion/)|[Solution](../../blob/master/EASY/src/easy/ZigZagConversion.java) | O(n) | O(n) | Easy | 
 |2|[Add Two Numbers](https://leetcode.com/problems/add-two-numbers/)|[Solution](../../blob/master/MEDIUM/src/medium/AddTwoNumbers.java) | O(n) | O(1) | Medium | LinkedList
 |1|[Two Sum](https://leetcode.com/problems/two-sum/)|[Solution](../../blob/master/EASY/src/easy/TwoSum.java)| O(n)/O(n^2)|O(1)/O(n) | Easy| HashMap