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Leetcode 171 Excel Sheet Column Number

发表于 更新于 分类于 Valine：
本文字数： 866 阅读时长 ≈ 1 分钟

Given a column title as appear in an Excel sheet, return its corresponding column number.

For example:

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2
3
4
5
6
7
8
A -> 1
B -> 2
C -> 3
...
Z -> 26
AA -> 27
AB -> 28 
...

Example 1:

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2
Input: "A"
Output: 1

Example 2:

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2
Input: "AB"
Output: 28

Example 3:

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2
Input: "ZY"
Output: 701

Constraints:

  • 1 <= s.length <= 7
  • s consists only of uppercase English letters.
  • s is between “A” and “FXSHRXW”.

26进制

本质上就是26进制. 只不过这种方式没法表示0. 因为是从1开始的

所以要注意计算的时候有int tmp = s.charAt(i) - 'A' + 1; 而不是int tmp = s.charAt(i) - 'A';

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class Solution {
    public int titleToNumber(String s) {
        if(s == null || "".equals(s))
            return 0;
        int ans = 0;
        for(int i = 0; i < s.length(); ++i)
        {
            ans *= 26;
            if(s.charAt(i) < 'A' || s.charAt(i) > 'Z'){
                throw new RuntimeException("string has non-uppercase char.");
            }
            int tmp = s.charAt(i) - 'A' + 1;
            ans += tmp;
        }
        return ans;
    }
}