Counting Comparisons in Insertion Sort

• First scan through the list requires N-1 comparisons

• Second scan through the list requires N-2 comparisons

• Third scan through the list requires N-3 comparisons

• etc.

• Last scan through the list requires 1 comparison

• Total number of comparisons:

  1 + 2 + ... + N-1 = N*(N-1)/2 ~ N * N / 2
  

• Therefore running time is proportional to N*N

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