LintCode-3.统计数字

统计数字

计算数字k在0到n中的出现的次数，k可能是0~9的一个值

样例

例如n=12，k=1，在 [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]，我们发现1出现了5次 (1, 10, 11, 12)

标签

枚举法

code

class Solution {
public:
    /*
     * param k : As description.
     * param n : As description.
     * return: How many k's between 0 and n.
     */
    int digitCounts(int k, int n) {
        // write your code here
        int res = 0;  
        int base = 1;

        if(n==0 && k==0)
            return 1; 
        
        while(n/base>0) {  
            int curBit = (n/base);  
            int low = n - (n/base)*base;  
            int high = n/(base*10);  
            if (curBit < k)  {  
                res += high*base;                         
            }
            else if (curBit == k) {  
                res += high*base+low+1;  
            }
            else {
                if(!(k==0 && high==0)) {  
                    res += (high+1)*base;  
                }  
            }  
            base *=10;  
        }  
        return res;
    }
};