171.excel表列序号.js

/*
 * @lc app=leetcode.cn id=171 lang=javascript
 *
 * [171] Excel表列序号
 *
 * https://leetcode-cn.com/problems/excel-sheet-column-number/description/
 *
 * algorithms
 * Easy (68.41%)
 * Likes:    185
 * Dislikes: 0
 * Total Accepted:    54.9K
 * Total Submissions: 80.3K
 * Testcase Example:  '"A"'
 *
 * 给定一个Excel表格中的列名称，返回其相应的列序号。
 * 
 * 例如，
 * 
 * ⁠   A -> 1
 * ⁠   B -> 2
 * ⁠   C -> 3
 * ⁠   ...
 * ⁠   Z -> 26
 * ⁠   AA -> 27
 * ⁠   AB -> 28 
 * ⁠   ...
 * 
 * 
 * 示例 1:
 * 
 * 输入: "A"
 * 输出: 1
 * 
 * 
 * 示例 2:
 * 
 * 输入: "AB"
 * 输出: 28
 * 
 * 
 * 示例 3:
 * 
 * 输入: "ZY"
 * 输出: 701
 * 
 * 致谢：
 * 特别感谢 @ts 添加此问题并创建所有测试用例。
 * 
 */

// @lc code=start
/**
 * @param {string} s
 * @return {number}
 */
var titleToNumber = function(s) {
    const charCodeBase = 'A'.charCodeAt(0) - 1;
    const n = s.length;
    let number = 0;

    /* 
     * Think of it as base 26. For example,
     * Column number of "AB" = 1 * 26^1 + 2 * 26^0 
     */
    for (let i = 0; i < n; i++)
        number += (s.charCodeAt(i) - charCodeBase) * Math.pow(26, n-i-1);
    
    return number;
};
// @lc code=end