PAT 1049 Counting Ones (30)
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.
Input Specification:
Each input file contains one test case which gives the positive N (<=2^30^).
Output Specification:
For each test case, print the number of 1's in one line.
Sample Input:
12
Sample Output:
5
#include<iostream> #include<vector> using namespace std; int main(){ int n; while(1){ cin>>n; if(n==-1) break; vector<int> v; v.push_back(0); for(int i=1; i<=n; i++){ int cnt=0, temp=i; while(temp){ if(temp%10==1) cnt++; temp/=10; } v.push_back(v[i-1]+cnt); } cout<<v[n]<<" "<<f(n)<<endl; } return 0; }
观察可以发现每一位1出现的次数和当前位左边的数有关 也和右边的数有关;
计算1的个数还与当前为的数有关
当前位为0的时候
当前位为1
当前位为12..9
1 #include<iostream> 2 #include<vector> 3 #include<cmath> 4 using namespace std; 5 6 int main(){ 7 int n; 8 cin>>n; 9 int cnt=0, cpy=n; 10 vector<int> v; 11 while(cpy){//求n的每一位数 12 v.push_back(cpy%10); 13 cpy /= 10; 14 } 15 cnt = n/10; 16 if(n%10>=1) cnt++; 17 int idx=2, coe=10; 18 while(idx<=v.size()){ 19 cnt += (n/(coe*10))*coe; 20 if(v[idx-1]>1) cnt += coe; 21 else if(v[idx-1]==1) cnt += (n%coe+1); 22 coe *= 10; 23 idx++; 24 } 25 cout<<cnt; 26 return 0; 27 }
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