Question

Formatted question description: https://leetcode.ca/all/171.html

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

For example:

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

Constraints:

1 <= columnTitle.length <= 7
columnTitle consists only of uppercase English letters.
columnTitle is in the range ["A", "FXSHRXW"].

Algorithm

It is equivalent to a problem of converting from hexadecimal to decimal. It is not difficult, as long as the conversion is bit by bit.

Code

public class Excel_Sheet_Column_Number {
    class Solution {
        public int titleToNumber(String s) {
            int result = 0;

            for (int i = 0; i < s.length(); i++) {
                result = result * 26 + (s.charAt(i) - 'A' + 1);
            }

            return result;
        }
    }
}

############

class Solution {
    public int titleToNumber(String columnTitle) {
        int res = 0;
        for (char c : columnTitle.toCharArray()) {
            res = res * 26 + (c - 'A' + 1);
        }
        return res;
    }
}

// OJ: https://leetcode.com/problems/excel-sheet-column-number/
// Time: O(N)
// Space: O(1)
class Solution {
public:
    int titleToNumber(string s) {
        int ans = 0;
        for (char c : s) ans = ans * 26 + (c - 'A' + 1);
        return ans;
    }
};

class Solution:
    def titleToNumber(self, columnTitle: str) -> int:
        res = 0
        for c in columnTitle:
            res = res * 26 + (ord(c) - ord('A') + 1)
        return res

############

class Solution(object):
  def titleToNumber(self, s):
    """
    :type s: str
    :rtype: int
    """
    letters = {"A": 1, "B": 2, "C": 3, "D": 4, "E": 5, "F": 6, "G": 7, "H": 8, "I": 9, "J": 10, "K": 11, "L": 12,
               "M": 13, "N": 14, "O": 15, "P": 16, "Q": 17, "R": 18, "S": 19, "T": 20, "U": 21, "V": 22, "W": 23,
               "X": 24, "Y": 25, "Z": 26}
    s = s.upper()
    ret = 0
    b = 0
    for c in reversed(s):
      ret += letters[c] * 26 ** (b)
      b += 1
    return ret

func titleToNumber(columnTitle string) int {
	res := 0
	for _, c := range columnTitle {
		res = res*26 + int(c-'A'+1)
	}
	return res
}

function titleToNumber(columnTitle: string): number {
    let res: number = 0;
    for (let char of columnTitle) {
        res = res * 26 + char.charCodeAt(0) - 64;
    }
    return res;
}

171 - Excel Sheet Column Number

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