Saturday, April 23, 2016

LeetCode 168 - Excel Sheet Column Title



Given a positive integer, return its corresponding column title as appear in an Excel sheet.
For example:
    1 -> A
    2 -> B
    3 -> C
    ...
    26 -> Z
    27 -> AA
    28 -> AB 

http://blog.welkinlan.com/2015/10/17/excel-sheet-column-number-title-leetcode-java/
    public int titleToNumber(String s) {
        int result = 0;
        for (int i = 0; i < s.length(); i++) {
            result = result * 26 + 1 + s.charAt(i) - 'A';
        }
        return result;
    }
http://blog.csdn.net/u012162613/article/details/42059591
因此可以将n转化为26进制表示的数,然后对每一位的数,根据『1->A,2->B,3->C....25->Y,26->Z』来转化。
当然,按照进制转换的方法(不断地除26取余数),不可能有26的余数,比如:52->(20)->AZ,此时余数是0,这种情况要特殊处理
string convertToTitle(int n) { string str; while(n){ int r=n%26; n=n/26; if(r==0){ //为26的整数倍,该位设置为Z,n减掉1 str+='Z'; n--; }else{ str+=('A'+r-1); } } //反转 string result; for(int i=str.size()-1;i>=0;i--){ result+=str[i]; } return result; }
http://www.programcreek.com/2014/03/leetcode-excel-sheet-column-title-java/
The key is n--. The minimum in 26-bit number is mapped to 1, not 0.
public String convertToTitle(int n) {
    if(n <= 0){
        throw new IllegalArgumentException("Input is not valid!");
    }
 
    StringBuilder sb = new StringBuilder();
 
    while(n > 0){
        n--;
        char ch = (char) (n % 26 + 'A');
        n /= 26;
        sb.append(ch);
    }
 
    sb.reverse();
    return sb.toString();
}
https://leetcode.com/discuss/19150/accepted-java-solution
public String convertToTitle(int n) { StringBuilder result = new StringBuilder(); while(n>0){ n--; result.insert(0, (char)('A' + n % 26)); n /= 26; } return result.toString(); }
https://leetcode.com/discuss/34526/share-my-java-solusion
public String convertToTitle(int n) { String res = ""; while(n != 0) { res = (char)('A' + (n - 1) % 26) + res; n = (n - 1) / 26; } return res; }
https://leetcode.com/discuss/19047/my-1-lines-code-in-java-c-and-python
return n == 0 ? "" : convertToTitle(--n / 26) + (char)('A' + (n % 26));
This is a very neat solution, but I am afraid that the time complexity of this solution (at least in python, as far as I can tell) is O((n/26)^2) because of the string concatenation in python. The time complexity of string concatenation is O(k) since it is immutable, k is the total length of the string. In your case, the function recurs roughly n/26 times, and in each recursion, there is a O(n/26) operation. So the total complexity of this method is roughly O(n^2) instead of O(n).
An improve could be that only use list which has a O(1) complexity appending, and only concatenate once at the end. The time complexity will be O(n), but the code need more lines.
http://www.jiuzhang.com/solutions/excel-sheet-column-title/
    string convertToTitle(int n) {
        if (n == 0) {
            return "";
        }
        return convertToTitle((n - 1) / 26) + (char)((n - 1) % 26 + 'A');
    }
http://blog.welkinlan.com/2015/10/17/excel-sheet-column-number-title-leetcode-java/
Given a positive integer, return its corresponding column title as appear in an Excel sheet.
    1 -> A
    2 -> B
    3 -> C
    ...
    26 -> Z
    27 -> AA
    28 -> AB

    public String convertToTitle(int n) {
        StringBuilder sb = new StringBuilder();
        while (n > 0) {
            int d = n % 26;
            n /= 26;
            if (d == 0) {
                sb.append('Z');
                n--;
            } else {
                sb.append((char)('A' + d - 1));
            }
        }
        return sb.reverse().toString();
    }

https://leetcode.com/discuss/24116/the-way-i-come-up-with-my-solution

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