Merge pull request #558 from Ananya-Misra/leetcode

Add Zig Zag Conversion

Author: smv1999

Dynamic Programming/zigzag_conversion.java

@@ -0,0 +1,97 @@
+// PROBLEM STATEMENT ALONG WITH TEST CASE
+// The string "PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)
+
+// P   A   H   N
+// A P L S I I G
+// Y   I   R
+// And then read line by line: "PAHNAPLSIIGYIR"
+
+// Write the code that will take a string and make this conversion given a number of rows:
+
+// string convert(string s, int numRows);
+ 
+
+// Example 1:
+
+// Input: s = "PAYPALISHIRING", numRows = 3
+// Output: "PAHNAPLSIIGYIR"
+// Example 2:
+
+// Input: s = "PAYPALISHIRING", numRows = 4
+// Output: "PINALSIGYAHRPI"
+// Explanation:
+// P     I    N
+// A   L S  I G
+// Y A   H R
+// P     I
+// Example 3:
+
+// Input: s = "A", numRows = 1
+// Output: "A"
+ 
+
+// Constraints:
+
+// 1 <= s.length <= 1000
+// s consists of English letters (lower-case and upper-case), ',' and '.'.
+// 1 <= numRows <= 1000
+
+import java.util.*;
+public class MyClass {
+    public static String convert(String s, int numRows) {
+        int flag = -1;
+
+        HashMap < Integer, String > map = new HashMap < > ();
+        int pos = 0;
+        String word = "";
+        if (numRows <= 1)
+            return s;
+        else {
+            // traversing in zig zag pattern and storing the data of each row in hash map as string
+            for (int x = 0; x < s.length(); x++) {
+                char ch1 = s.charAt(x);
+                String ch = Character.toString(ch1);
+
+                if (pos == (numRows - 1) || flag == 1 && pos > 0) {
+                    flag = 1;
+                    if (map.containsKey(pos)) {
+                        String a = map.get(pos);
+                        // concatinating the previous word along with new character
+                        String w = a + ch;
+                        map.put(pos, w);
+                    } else {
+                        map.put(pos, ch);
+                    }
+                    // once reached the end of the row start moving upwards i.e decreasing the key in hash map
+                    pos--;
+                } 
+                else if (pos == 0 || flag == 0) {
+                    flag = 0;
+                    // check if the key in hash map has some data present
+                    if (map.containsKey(pos)) {
+                        String a = map.get(pos);
+                        String w = a + ch;
+                        map.put(pos, w);
+                    } else {
+                        map.put(pos, ch);
+                    }
+                    // keep increasing the key i.e pos in hash map till we reach at the end of the row
+                    pos++;
+                }
+            }
+            for (Map.Entry < Integer, String > e: map.entrySet())
+                // concatinate the values of each row of hash map
+                word = word + e.getValue();
+
+            return word;
+        }
+    }
+    //main function
+    public static void main(String args[]) {
+        Scanner sc = new Scanner(System.in);
+        String s = sc.next();
+        int rows = sc.nextInt();
+        System.out.println(convert(s, rows));
+
+    }
+}