PAT a1010题解

#include <cstdio>#include <cstring>#include <algorithm>using namespace std;typedef long long LL;LL Map[256];LL inf = (1LL << 63) - 1;void init(){for(char c = '0'; c <= '9'; c++){Map[c] = c - '0';}for(char c = 'a'; c <= 'z'; c++){Map[c] = c - 'a' + 10;}} LL convertNum10(char a[], LL radix, LL t){LL ans = 0;int len = strlen(a);for(int i = 0; i < len; i++){ans = ans * radix + Map[a[i]];if(ans < 0 || ans > t) return -1;}return ans;} int cmp(char N2[], LL radix, LL t){int len = strlen(N2);LL num = convertNum10(N2, radix, t);if(num < 0) return 1;if(t > num) return -1;else if(t == num) return 0;else return 1; }LL binarySearch(char N2[], LL left, LL right, LL t){LL mid;while(left <= right){mid = (left+ right) / 2;int flag = cmp(N2, mid, t);if(flag == 0) return mid;else if(flag == -1) left = mid + 1;else right = mid - 1;}return -1;}int findLargestDigit(char N2[]){int ans = -1, len = strlen(N2);for(int i = 0; i < len; i++){if(Map[N2[i]] > ans){ans = Map[N2[i]];}}return ans + 1;}char N1[20], N2[20], temp[20];int tag, radix;int main(){init();scanf("%s %s %d %d", N1, N2, &tag, &radix);if(tag == 2){strcpy(temp, N1);strcpy(N1, N2);strcpy(N2, temp);} LL t = convertNum10(N1, radix, inf);LL low = findLargestDigit(N2);LL high = max(low, t) + 1;LL ans = binarySearch(N2, low, high, t);if(ans == -1) printf("Impossible\n");else printf("%lld\n", ans);return 0;}