Crossing Bridge Problem

#107

There are 4 friends who want to cross the bridge. There is only 1 lamp with them which is needed to cross the bridge and only 2 persons can cross the bridge at a time.
The time taken to cross the bridge by each person is 1 min, 2 min, 5 min and 10 min respectively.
How can they cross the bridge if the bridge is going to break in only 17 minutes ?

  Difficulty Level - 3/5

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  Solution : 

   (1,2) 1 returns (3 mins)
   (5,10) 2 returns (12 mins)
   (1,2) i.e. 2 mins .....
   So overall 17 mins.
OR
   (1,2) 2 returns (4 mins)
   (5,10) 1 returns (11 mins)
   (1,2) i.e. (2 mins)
    So overall 17 mins.