Daily practice (41): Excel table column names

---

title: Daily practice (41): Excel table column name

categories:[Swords offer]

tags:[Daily practice]

date: 2022/04/13

---

Daily practice (41): Excel table column names

Given an integer columnNumber, return its corresponding column name in the Excel table.

E.g:

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

Example 1:

Input: columnNumber = 1

Output: "A"

Example 2:

Input: columnNumber = 28

Output: "AB"

Example 3:

Input: columnNumber = 701

Output: "ZY"

Example 4:

Input: columnNumber = 2147483647

Output: "FXSHRXW"

hint:

1 <= columnNumber <= 231 - 1

Source: LeetCode

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

Method 1: Hexadecimal conversion from 1

Thought analysis

The normal 26 hexadecimal display number should be 0-25, and this question is 1-26, then subtract one before processing each digit, which can become a normal hexadecimal conversion operation.

 string convertToTitle(int columnNumber) {
    string ans;
    do {
        columnNumber--;
        ans = char(columnNumber % 26 + 'A') + ans;//得到字符列名称
        columnNumber /= 26;
    } while(columnNumber > 0);
    return ans;
}

Method 2: Remainder + Invert

Thought analysis

When the remainder is 0, we can't take @ but should take Z

 string convertToTitle(int columnNumber) {
    string ans;
    while (columnNumber) {
        int remainder = columnNumber % 26;
        if (remainder == 0) { //如果余数是0，就像上一位借个1（26）出来，让余数强行等于26
            remainder = 26;
            columnNumber -= 26;
        }
        ans.push_back(remainder + 'A' - 1);
        columnNumber /= 26;
    }
    reverse(ans.begin(), ans.end());//字符串倒序
    return ans;
}