我也来刷LeetCode——3、Add Digits

　　唉，做完这道题目后，有种羞愧无比的感觉，果然还是读书太少。。。

　　什么意思呢？就像这道题目一样，要求你编程计算出从1加到100的结果。于是你用循环从1累加到100，结果为5050。而大家都知道，从数学上的角度来解答，结果就是（a[1]+a[n]）* n / 2。

　　LeetCode上面的这道【Add Digits】题，其实是道数学题。它这个求解的结果，在数学上称为数根。

　　原题大概意思是这样，给定一个正整数，循环累加它的各位，直到结果为一位数。如 num 是38，计算的过程是 3+8=11，1+1=2，2为一位数，即为结果。而实际上这个结果就是这个数的数根。

　　一个数的数根，用数学公式来表达就是 f(n) =(n - 1) % 9 + 1，这个公式的证明不难，可以看这里。

　　最后~还是觉得很惭愧。。。

1 class Solution {
2 public:
3     int addDigits(int num) {
4         return (num -1) % 9 + 1;
5     }
6 };

时间： 2024-08-29 08:40:53

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