Here is the problem statement
http://www.spoj.com/problems/FACEFRND/
Some commets that you can use STL set to solve, of course its a good choice but we can do it in a simpler way(without using STL). Just because the numbers are 4 digit numbers , we can just keep a boolean array , and every time we read a number A (the number of a friend's friend) we mark Mark[A] as true. Then at the end we loop from 1000 to 9999 and calculate the number of marked spots. Its is shorter when you are using STL but this way is safer :) .
http://www.spoj.com/problems/FACEFRND/
Some commets that you can use STL set to solve, of course its a good choice but we can do it in a simpler way(without using STL). Just because the numbers are 4 digit numbers , we can just keep a boolean array , and every time we read a number A (the number of a friend's friend) we mark Mark[A] as true. Then at the end we loop from 1000 to 9999 and calculate the number of marked spots. Its is shorter when you are using STL but this way is safer :) .
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