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; }