Add solution #171

Author: JoshCrozier

README.md

@@ -163,6 +163,7 @@
 167|[Two Sum II - Input Array Is Sorted](./0167-two-sum-ii-input-array-is-sorted.js)|Easy|
 168|[Excel Sheet Column Title](./0168-excel-sheet-column-title.js)|Easy|
 169|[Majority Element](./0169-majority-element.js)|Easy|
+171|[Excel Sheet Column Number](./0171-excel-sheet-column-number.js)|Easy|
 179|[Largest Number](./0179-largest-number.js)|Medium|
 187|[Repeated DNA Sequences](./0187-repeated-dna-sequences.js)|Medium|
 189|[Rotate Array](./0189-rotate-array.js)|Medium|

solutions/0171-excel-sheet-column-number.js

@@ -0,0 +1,18 @@
+/**
+ * 171. Excel Sheet Column Number
+ * https://leetcode.com/problems/excel-sheet-column-number/
+ * Difficulty: Easy
+ *
+ * Given a string columnTitle that represents the column title as appears in
+ * an Excel sheet, return its corresponding column number.
+ */
+
+/**
+ * @param {string} columnTitle
+ * @return {number}
+ */
+var titleToNumber = function(columnTitle) {
+  return columnTitle.split('').reduce((result, c, i) => {
+    return result + (c.charCodeAt() - 64) * Math.pow(26, columnTitle.length - (i + 1));
+  }, 0);
+};