start:   45000  21000  70000  28000 136500  30000
linear search for 28000: index 3
pass 1:  21000  45000  28000  70000  30000 136500
pass 2:  21000  28000  45000  30000  70000 136500
pass 3:  21000  28000  30000  45000  70000 136500
pass 4:  21000  28000  30000  45000  70000 136500
binary search for 70000:
  low=0 mid=2 high=5 looks at 30000
  low=3 mid=4 high=5 looks at 70000
found at index 4
binary search for 50000:
  low=0 mid=2 high=5 looks at 30000
  low=3 mid=4 high=5 looks at 70000
  low=3 mid=3 high=3 looks at 45000
found at index -1
