题目链接：http://codeforces.com/problemset/problem/328/A
这道题目wa了一次，注意这句话：
You should also print 42 if the next element of progression is not integer. So answer is always integer.
然后就可以了。
1 /* 2 ID: zypz4571 3 LANG: C++ 4 TASK: iqtest.cpp 5 */ 6 7 #include <cstdio> 8 #include <cstdlib> 9 #include <cstring> 10 #include <cmath> 11 #include <cctype> 12 #include <algorithm> 13 #include <queue> 14 #include <set> 15 #include <queue> 16 #include <list> 17 #include <map> 18 #define INF 0x3f3f3f3f 19 #define mid int m=(l+r)/2 20 using namespace std; 21 int main ( int argc, char *argv[] ) 22 { 23 #ifndef ONLINE_JUDGE 24 freopen("in.txt", "r", stdin); 25 #endif 26 int a, b, c, d; scanf("%d%d%d%d", &a,&b,&c,&d); 27 if(b-a==c-b&&c-b==d-c) printf("%d ",2*d-c); 28 else if (b*b==a*c&&b*d==c*c&&(d*d%c==0)) printf("%d ",d*d/c); 29 else printf("42 "); 30 return EXIT_SUCCESS; 31 } /* ---------- end of function main ---------- */
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