Multiply Strings || Excel Sheet Column Title

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Multiply Strings

Question

Given two numbers represented as strings, return multiplication of the numbers as a string.

Note:

  • The numbers can be arbitrarily large and are non-negative.
  • Converting the input string to integer is NOT allowed.
  • You should NOT use internal library such as BigInteger.

Analysis

https://discuss.leetcode.com/topic/30508/easiest-java-solution-with-graph-explanation

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Code

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public String multiply(String num1, String num2) {
    int m = num1.length(), n = num2.length();
    int[] pos = new int[m + n];
   
    for(int i = m - 1; i >= 0; i--) {
        for(int j = n - 1; j >= 0; j--) {
            int mul = (num1.charAt(i) - '0') * (num2.charAt(j) - '0'); 
            int p1 = i + j, p2 = i + j + 1;
            int sum = mul + pos[p2];
            pos[p1] += sum / 10;
            pos[p2] = (sum) % 10;
        }
    }  
    
    StringBuilder sb = new StringBuilder();
    for(int p : pos) if(!(sb.length() == 0 && p == 0)) sb.append(p);
    return sb.length() == 0 ? "0" : sb.toString();
}

Excel Sheet Column Title

Question

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

For example:

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

Analysis

26进制转10进制

Code

Mine

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public class Solution {
    public String convertToTitle(int n) {
        StringBuilder res=new StringBuilder();
        int remain=0;
        while(n>26){
            remain=n%26;
            if(remain==0){
                res.insert(0,'Z');
                n--;
            }else{
                res.insert(0,(char)(remain+64));
            }
            n/=26;
        }
        res.insert(0,(char)(n+64));
        return res.toString();
    }
}

Better

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public class 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();
    }
}

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