LeetCode Js-171. Excel Sheet Column Number

    AllenLi
    LeetCode Js-String

    Given a string columnTitle that represents the column title as appears in an Excel sheet, return its corresponding column number.

    給予一個字串 columnTitle，然後它代表欄位的名稱出現在excel表中。回傳對應的欄位數值。

    Example 1:

    Input: columnTitle = "A"
Output: 1

    Example 2:

    Input: columnTitle = "AB"
Output: 28

    Example 3:

    Input: columnTitle = "ZY"
Output: 701

    solution:
    1. 宣告 sum 作為數值計算的變數，以及 EXP 作為數值的次方。
    2. 透過用字串位數來進行迴圈。
    3. 運用 charCodeAt() 來對 columnTitle 的單一字串進行數值轉換。

    依據 ANSI CODE 的轉換，如下：
A = 65,
B = 66,
C = 67
 ...
X = 88
Y = 89
Z = 90

    4. 最後透過 EXP 與「sum += 」來完成數值加總。

    A = (65 - 64) * (26 ** 0) //1 * 1 = 1

"A" A = (65 - 64) * (26 ** 1) //1 * 26 = 26
 A "A" = (65 - 64) * (26 ** 0) //1 * 1 = 1
=> 26 + 1 = 27

    Code 1:

    var titleToNumber = function(columnTitle) {
    let sum = 0;
    for (let i = 0; i < columnTitle.length; i++) {
        let EXP = columnTitle.length - 1 - i;
        sum += (columnTitle[i].charCodeAt(0) - 64) * (26 ** EXP);
    }
    
    return sum;
};

    FlowChart:
    Example 1

    Input: columnTitle = "A"
EXP = 26 ** 0

A = (65 - 64) * (26 ** 0) //1 * 1 = 1

    Example 2

    Input: columnTitle = "AB"
EXP = (i = 0) * 26 ** 1 + (i = 1) * 26 * 0

"A" B = (65 - 64) * (26 ** 1) //1 * 26 = 26
 A "B" = (66 - 64) * (26 ** 0) //2 * 1 = 2
=> 26 + 2 = 28

    Example 3

    Input: columnTitle = "ZY"
EXP = (i = 0) * 26 ** 1 + (i = 1) * 26 * 0

"Z" Y = (90 - 64) * (26 ** 1) //26 * 26 = 676
 Z "Y" = (89 - 64) * (26 ** 0) //25 * 1 = 25
=> 676 + 25 = 701

    charCodeAt()

    "ABC".charCodeAt(0) // returns 65:"A"

"ABC".charCodeAt(1) // returns 66:"B"

"ABC".charCodeAt(2) // returns 67:"C"

"ABC".charCodeAt(3) // returns NaN

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