Question

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

 171	Excel Sheet Column Number

 Given a column title as appear 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: "A"
 Output: 1

 Example 2:

 Input: "AB"
 Output: 28

 Example 3:

 Input: "ZY"
 Output: 701 (26*26+25)

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

Java

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;
        }
    }
}

// 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(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

171 - Excel Sheet Column Number

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