The task is simple: given any positive integer N, you are supposed to count the total number of 1‘s in the decimal form of the integers from 1 to N. For example, given N being 12, there are five 1‘s in 1, 10, 11, and 12.
Each input file contains one test case which gives the positive N (≤).
For each test case, print the number of 1‘s in one line.
12
5
题目分析：一道数学题 题目据说是《编程之美》上的一道题
具体的推法好像很麻烦的样子 之后有时间会看看
1 #define _CRT_SECURE_NO_WARNINGS 2 #include <climits> 3 #include<iostream> 4 #include<vector> 5 #include<queue> 6 #include<map> 7 #include<set> 8 #include<stack> 9 #include<algorithm> 10 #include<string> 11 #include<cmath> 12 using namespace std; 13 14 int main() 15 { 16 int N; 17 cin >> N; 18 int count = 0,left=0,right=0,now=1,a=1; 19 while (N/a) 20 { 21 left = N / (a * 10); 22 now = N / a % 10; 23 right = N % a; 24 if (now == 0)count += left * a; 25 else if (now ==1)count += left * a + right + 1; 26 else if (now > 1)count += (left + 1) * a; 27 a *= 10; 28 } 29 cout << count; 30 }
原文：https://www.cnblogs.com/57one/p/12044478.html
