长期更新,对使用 Java 刷 LeetCode 过程中一些有趣的题的感想和启发。 解题源代码仓库
题目
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
…
Example 1:
Input: 1
Output: “A”
Example 2:
Input: 28
Output: “AB”
Example 3:
Input: 701
Output: “ZY”
我的思路
这道题我的思路是先通过等比数列算出来结果有多少位,然后在一位一位的算出来字符。具体的算每一位的方式就是算第 m
位的时候用 n - 26^{n-1}
,再从 alphaArr
中提取。结果就是当 n = 10000001
的时候,TLE。。。
我的代码
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//解决方法
class Solution {
String[] alphaArr = new String[]{"","A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z"};
public String convertToTitle(int n) {
int bit = findBit(n);
int a = n;
int b,c;
String output = "";
while(bit > 0){
b = myPow(bit - 1);
c = n / b;
if (c > 26) c = 26
else {
if (n%26 == 0 && bit != 1) c -= 1;
}
output = output + alphaArr[c];
bit = bit - 1;
n -= b * c;
}
return output;
}
public int findBit(int n){
int i = 1;
while (calcu(i) < n){
i++;
}
return i;
}
public int calcu(int i){
return (26*(1 - myPow(i)))/(-25);
}
public int myPow(int upper){
int output = 1;
int lower = 26;
for (int i = 0;i < upper ; i++) {
output *= lower;
}
return output;
}
}
OMG OTL!!!
最后我想了很久还是没有想出来好的解法,知道是要用递归算法但不知道怎么用。于是只好去翻一翻 discuss
,结果。。。
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//My 1 lines code in Java, C++, and Python
return n == 0 ? "" : convertToTitle(--n / 26) + (char)('A' + (n % 26));
惊呆了。。。自己真的太辣鸡了。
本文作者 Auther:Soptq
本文链接 Link: https://soptq.me/2018/10/10/leetCode168/
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