数学
容易忘
class Solution {
public int countDigitOne(int n) {
int digit = 1, res = 0;
int high = n / 10, cur = n % 10, low = 0;
while(high != 0 || cur != 0){
if(cur == 0) res += high * digit;
else if(cur == 1) res += high * digit + low + 1;
else res += (high + 1) * digit;
low += cur * digit;
cur = high % 10;
high /= 10;
digit *= 10;
}
return res;
}
}