PAT Advanced Level-1010. Radix (25)

#include <stdio.h>  
#include <string.h>  
  
long num2Dec(char *,int);//转换成10进制数据  
long findLowRadix(char *);//寻找最低进制数  
long binarysearch(char *,long ,long, long);  
int main()  
{  
    char N1[11],N2[11];  
    int tag,radix;  
    long target = 0L,result=0L;  
    long least;//进制最小  
    long most;//进制最大  
    scanf("%s%s",N1,N2);  
    scanf("%d%d",&tag,&radix);  
  
    if(1 == tag)  
    {  
        target = num2Dec(N1,radix);  
        least=findLowRadix(N2);  
        most = (target + 1 > least + 1) ? target +1 :least +1;   
        result = binarysearch(N2,least,most,target);  
        if(result == -1)  
            printf("Impossible");  
        else  
            printf("%d\n",result);  
    }else if(2 == tag)  
    {  
        target = num2Dec(N2,radix);  
        least=findLowRadix(N1);  
        most = (target + 1 > least + 1) ? target +1 :least +1;   
        result = binarysearch(N1,least,most,target);  
        if(result == -1)  
            printf("Impossible");  
        else  
            printf("%d\n",result);  
    }  
  
    return 0;  
}  
long num2Dec(char *p,int radix)  
{  
    int len = strlen(p);  
    int m=1,num=1,sum=0;  
    int i=0;  
    for(i=len-1;i>=0;i--)  
    {  
        if(p[i]>='a' && p[i]<='z')  
            num = p[i]-'a' + 10;  
        else if(p[i] >= '0' && p[i] <= '9')  
            num = p[i]-'0';  
        sum += num*m;  
        m*=radix;  
    }  
    return sum;  
}  
  
//ab:最小就是12进制  69：最小就是10进制  
long findLowRadix(char *p)  
{  
    long len=strlen(p),low=0,num=0,i=0;    
  
    for(i=len-1;i>=0;i--)    
    {    
        if(p[i]>='a'&&p[i]<='z')    
            num= p[i] - 'a' + 10;    
        else if(p[i]>='0'&& p[i]<='9')    
            num=p[i] - '0';    
        if(num+1>low)    
            low=num+1;    
    }    
  
    return low;    
}  
long binarysearch(char *p,long low,long high,long target)  
{  
    long mid=low,tmp=0;  
    while(low<=high)  
    {  
        tmp = num2Dec(p,mid);  
        if(tmp > target)  
            high=mid-1;  
        else if(tmp < target)  
            low = mid+1;  
        else   
            return low;  
        mid = (low+high)/2;  
    }  
    return -1;  
}