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 

這就是個(gè)進(jìn)制轉(zhuǎn)換，把每位讀出來乘上對(duì)應(yīng)的26的次方數(shù)。

/**
 * @param {string} s
 * @return {number}
 */
var titleToNumber = function(s) {
    var num = s.length;
    var result = 0;
    for (var i = 0 ; i<num ;i++) {
        result += (s[i].charCodeAt(0)-64)*Math.pow(26,num-1-i);
    }
    return result;
};

還有個(gè)不用乘方的辦法：

/**
 * @param {string} s
 * @return {number}
 */
var titleToNumber = function(s) {
    var num = s.length;
    var result = 0;
    for (var i = 0 ; i<num ;i++) {
          result = result * 26 + (s.charCodeAt(i) - 64);
    }
    return result;
};