1010.Radix (25)...to be continued...

/**
* pat-al-1010
* 2017-02-15
* Cpp version
* Author: fengLian_s
*/
#include<stdio.h>
#include<string.h>
#include<algorithm>
#include<limits.h>
using namespace std;
int map[256];
long long turn2Decimal(char n[], int radix)
{
long long ans = 0;
int len = strlen(n);
for(int i = 0;i < len;i++)
{
ans = ans * radix + map[n[i]];
}
if(ans < 0 || ans > LLONG_MAX)
return -1;
return ans;
}
long long findLargestDigit(char n[])
{
int len = strlen(n);
int max = -1;
for(int i = 0;i < len;i++)
{
if(max < map[n[i]])
max = map[n[i]];
}
return max+1;
}
int cmp(long long num2, long long num1)
{
if(num2 < 0)
return 1;
if(num2 < num1)
return -1;
return (num2 == num1) ? 0 : 1;
}
long long binarySearch(char n[], long long low, long long high, long long num1)
{
long long mid;
while(low <= high)
{
mid = (low + high) / 2;
int flag = cmp(turn2Decimal(n, mid), num1);
if(flag == 0)
return mid;
else if(flag == 1)
high = mid - 1;
else
low = mid + 1;
}
return -1;
}
int main()
{
for(char c = '0';c <= '9';c++)
map[c] = c - '0';
for(char c = 'a';c <= 'z';c++)
map[c] = c - 'a' + 10;
freopen("in.txt", "r", stdin);
char n1[12], n2[12];
int tag, radix;
scanf("%s%s%d%d", n1, n2, &tag, &radix);
//printf("%s %s %d %d\n", n1, n2, tag, radix);
if(tag == 2)//交换，保证n1是radix进制的
{
swap(n1, n2);
}
long long num1 = turn2Decimal(n1, radix);
long long low = findLargestDigit(n2);
long long high = max(num1, low) + 1;//问题：没想清楚为什么
long long result = binarySearch(n2, low, high, num1);
if(result == -1)
printf("Impossible\n");
else
printf("%lld\n", result);
}