feat: Added zig-zag-converstion for js

.gitignore

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+/.gtm/

zig-zag-conversion/js/index.js

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+/*
+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
+*/
+
+/**
+ * @param {string} s
+ * @param {number} numRows
+ * @return {string}
+ */
+const convert = (s, numRows) => {
+  const pattern = [];
+  let x = 0;
+  let y = 0;
+  let goingDown = true;
+  for(let i = 0; i < s.length; i++){
+    if (y === numRows  && goingDown) {
+      y = numRows - 2;
+      x++;
+      goingDown = false;
+    }
+    if (y == -1 && !goingDown){
+      y = 1;
+      x++;
+      goingDown = true;
+    }
+
+    if (!pattern[x]){
+      pattern[x] = [];
+    }
+    pattern[x][y] = s[i];
+    if (goingDown){
+      y++;
+    } else {
+      y--;
+    }
+  }
+
+  let col = 0;
+  let output='';
+  let j = 0;
+  // Time complexity: O(n)
+  while (j < s.length) {
+    // Reset col counter to 0 if at the last col
+    if (col === pattern.length) {
+      col = 0;
+    }
+    // Remove empty cols from list then skip
+    if (!pattern[col] || pattern[col].length === 0){
+      pattern.splice(col, 1);
+      continue;
+    }
+
+    const char = pattern[col][0];
+    // Add character to output and increment char counter
+    // Don't increment if character is null
+    // char can be null since we were not adding elements in every index
+    if (char) {
+      output+=char;
+      j++;
+    }
+    pattern[col].shift();
+    col++;
+  }
+  return output;
+};
+
+let s, numRows;
+/* Test Case 1
+ * Input s = "PAYPALISHIRING", numRows = 3
+ * Output: "PAHNAPLSIIGYIR"
+ */
+
+s = 'PAYPALISHIRING';
+numRows = 3;
+console.log(convert(s, numRows));
+
+/* Test Case 2
+ * Input: s = "PAYPALISHIRING", numRows = 4
+ * Output: "PINALSIGYAHRPI"
+ */
+s =  'PAYPALISHIRING';
+numRows = 4;
+console.log(convert(s, numRows));
+
+/* Test Case 3
+ * Input: s = "AB", numRows = 1
+ * Output: "AB"
+ */
+s =  'AB';
+numRows = 1;
+console.log(convert(s, numRows));