pat1049

http://blog.csdn.net/makecontral/article/details/38538357 

这么神奇的规律，真心看不出来啊T_T

#include<stdio.h>int CountOnes(int n){int count = 0;int factor = 1;int higher,lower,cur;while(n/factor != 0){higher = n/(factor*10);lower = n - (n/factor)*factor;cur = (n/factor)%10;switch (cur){case 0:count += higher*factor;break;case 1:count += higher*factor + lower +1;break;default:count += higher*factor + factor;}factor = factor * 10;}return count;}int main(){int n;scanf("%d",&n);printf("%d\n",CountOnes(n));return 0;}