There are 15 nodes in the min-heap, there are 7 internal nodes and 8 leaf nodes. suppose keys are 1, 2, 3, ........ 15
1 to 7 are internal nodes and 8 to 15 are leaf nodes.
there are 4 levels in the tree, and following are the possible min-heap trees:
First Case: 2!*4!*8! = 1935360
Second Case: 8!*(4!-3!*2)2!
Third case: 8!*(2!*2!)*2!
Total: first case + second case + third case = 3225600