LeetCode-400. Nth Digit

Description

Note

Example 1

Example 2

Solution 1(C++)

class Solution {
public:
int findNthDigit(int n) {
// step 1. calculate how many digits the number has.
long base = 9, digits = 1;
while (n - base * digits > 0)
{
n -= base * digits;
base *= 10;
digits ++;
}

// step 2. calculate what the number is.
int index = n % digits;
if (index == 0)
index = digits;
long num = 1;
for (int i = 1; i < digits; i ++)
num *= 10;
num += (index == digits) ? n / digits - 1 : n / digits;;

// step 3. find out which digit in the number is we wanted.
for (int i = index; i < digits; i ++)
num /= 10;
return num % 10;
}
};

算法分析

程序分析