add Easy_171_Excel_Sheet_Column_Number

Easy_171_Excel_Sheet_Column_Number.js

@@ -0,0 +1,31 @@
+/**
+ * Given a column title as appear in an Excel sheet, return its corresponding column number.
+
+ For example:
+
+ A -> 1
+ B -> 2
+ C -> 3
+ ...
+ Z -> 26
+ AA -> 27
+ AB -> 28
+
+ */
+
+/**
+ * @param {string} s
+ * @return {number}
+ */
+var titleToNumber = function (s) {
+
+    var num = 0;
+    var aCode = 'A'.charCodeAt(0);
+    for (var i = 0; i < s.length; i++) {
+        var n = 1 + s.charCodeAt(i) - aCode;
+        num = num * 26 + n;
+    }
+    return num;
+};
+
+console.log(titleToNumber('AA'));