题目大意：从1开始往后写数字，构成一个如下的字符串 123456789101112... 。求第n位的数字是多少。
找规律，按数字的位数可以构建一个类似杨辉三角的东西，求出第n位是哪个数的第几位即可。
1 #include <cstdio> 2 #include <cmath> 3 4 int main() 5 { 6 #ifdef LOCAL 7 freopen("in", "r", stdin); 8 #endif 9 int table[9] = {0}; 10 int base = 9; 11 for (int i = 1; i <= 8; i++) 12 { 13 table[i] = i * base; 14 base *= 10; 15 } 16 for (int i = 1; i <= 8; i++) 17 table[i] += table[i-1]; 18 int n; 19 while (scanf("%d", &n) != EOF) 20 { 21 int k = 1; 22 while (table[k] < n) k++; 23 double t1 = 1.0 * (n - table[k-1]) / k; 24 int offset = (int)ceil(t1); // n is offset-th num of k-th row 25 int t2 = (n - table[k-1] - 1) % k + 1; // the t2-th digit of the num 26 int t3 = 0; 27 for (int i = 1; i <= k-1; i++) 28 t3 = t3*10 + 9; 29 int m = t3 + offset; // the compete num 30 for (int i = 0; i < k-t2; i++) m /= 10; 31 printf("%d ", m % 10); 32 } 33 return 0; 34 }