整数中1出现的次数
求出1~13的整数中1出现的次数,并算出100~1300的整数中1出现的次数?为此他特别数了一下1~13中包含1的数字有1、10、11、12、13因此共出现6次,但是对于后面问题他就没辙了。ACMer希望你们帮帮他,并把问题更加普遍化,可以很快的求出任意非负整数区间中1出现的次数。
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1 #include <string.h> 2 class Solution { 3 public: 4 int NumberOf1Between1AndN_Solution(int n) 5 { 6 if(n<=0) return 0; 7 char strN[50]; 8 sprintf(strN,"%d",n); 9 return NumberOf(strN); 10 } 11 int NumberOf(const char* strN){ 12 if(!strN || *strN < '0' || *strN > '9' || *strN == '\0') return 0; 13 14 int first = *strN - '0'; 15 unsigned int length = static_cast<unsigned int>(strlen(strN)); 16 if(length == 1 && first == 0) return 0; 17 if(length == 1 && first > 0) return 1; 18 19 int numFirstDigit = 0; 20 if(first > 1) numFirstDigit = PowerBase10(length-1); 21 else if(first==1) numFirstDigit = atoi(strN + 1) +1; 22 23 int numOtherDigits = first * (length-1) * PowerBase10(length-2); 24 int numRecursive = NumberOf(strN + 1); 25 26 return numFirstDigit + numOtherDigits + numRecursive ; 27 } 28 int PowerBase10(int n){ 29 int result = 1; 30 for(int i=0; i<n; i++) result *= 10; 31 return result; 32 } 33 };