全国信息学奥林匹克联赛（NOIP2010）复赛 1．数字统计 解题报告

 

 

 

方法一：穷举

 

///伟人 E-mail:[e-mail] QQ:270173053 欢迎交流//#include<stdio.h>int main(){unsigned int L,R,i,count=0,temp;FILE *in,*ou;if((in=fopen("two.in","r"))==NULL){printf("Can not open the input file.");exit(0);}if((ou=fopen("two.ou","w"))==NULL){printf("Can not open the output file.");exit(0);}fscanf(in,"%u%u",&L,&R);for(i=L;i<=R;i++){temp=i;while(temp!=0){if(temp%10==2) count++;temp=temp/10;}}fprintf(ou,"%u",count);fclose(in);fclose(ou);return 0;} 

 

方法二：从数学上分析

//伟人 E-mail:[e-mail] QQ:270173053 欢迎交流//#include<stdio.h>int Get2Count(unsigned int N){unsigned int p=1,count=0,right=0,left=N,current;while(left!=0){current=left%10;left=left/10;if(current<2){count+=left*p;}else if(current==2){count+=left*p+right+1;}else count+=(left+1)*p;right=right*10+current;p*=10;}return count;}int main(){unsigned int L,R;FILE *in,*ou;if((in=fopen("two10.in","r"))==NULL){printf("Can not open the input file.");exit(0);}if((ou=fopen("two.ou","w"))==NULL){printf("Can not open the output file.");exit(0);}fscanf(in,"%u%u",&L,&R);fprintf(ou,"%u",Get2Count(R)-Get2Count(L));fclose(in);fclose(ou);return 0;}