The digital root of a positive integer is found by summing the digits of the integer. If the resulting value is a single digit then that digit is the digital root. If the resulting value contains two or more digits, those digits are summed and the process is repeated. This is continued as long as necessary to obtain a single digit.

For example, consider the positive integer 24. Adding the 2 and the 4 yields a value of 6. Since 6 is a single digit, 6 is the digital root of 24. Now consider the positive integer 39. Adding the 3 and the 9 yields 12. Since 12 is not a single digit, the process must be repeated. Adding the 1 and the 2 yeilds 3, a single digit and also the digital root of 39.

这个题一开始我用的是int类型没考虑到数字特别大的情况,参考了神犇的解题报告后发现其实要用字符串来解决,而且是数论中的一条基本定理,我还循环折腾半天
Digtial Roots=(sum-1)%9+1
看来人丑还是要多读书

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