Daily practice (42): Excel sheet serial number

---

title: Daily practice (42): Excel sheet serial number

categories:[Swords offer]

tags:[Daily practice]

date: 2022/04/14

---

Daily practice (42): Excel sheet serial number

Gives you a string columnTitle representing the column name in the Excel table. Returns the column sequence number corresponding to the column name.

E.g:

A -> 1
B -> 2
C -> 3
...
Z -> 26
AA -> 27
AB -> 28
...

Example 1:

Input: columnTitle = "A"

output: 1

Example 2:

Input: columnTitle = "AB"

Output: 28

Example 3:

Input: columnTitle = "ZY"

Output: 701

hint:

1 <= columnTitle.length <= 7

columnTitle consists of uppercase English only

columnTitle is in range ["A", "FXSHRXW"]

Source: LeetCode

Link: https://leetcode-cn.com/problems/excel-sheet-column-number

Method 1: Base conversion (front to back)

Thought analysis

This question requires converting the column names in the Excel table to the corresponding column numbers. Since the column name of the Excel table consists of uppercase letters, there are 26 uppercase letters, so the column name

Indicates that the essence is 26 hexadecimal, and it is necessary to convert 26 hexadecimal to decimal.

Hexadecimal conversion to get the value according to the ASCII code.

 int titleToNumber(string columnTitle) {
    int ans = 0;
    for (char c : columnTitle) {
        int k = c - 'A' + 1;
        ans = ans * 26 + k;
    }
    return ans;
}

Method 2: Base conversion (from back to front)

Thought analysis

Hexadecimal conversion to get the value according to the ASCII code.

 int titleToNumber(string columnTitle) {
    int ans = 0;
    long multiple = 1;
    int n = columnTitle.length() - 1;
    for (int i = n; i >= 0; --i) {
        int k = columnTitle[i] - 'A' + 1;
        ans += k * multiple;
        multiple *= 26;
    }
    return ans;
}