Derive one giant overlap

onegiantoverlap.py

def mergeIntervals(arr):
  sorted(arr)
  index=0
  for i in range(len(arr)):
    if(index!=0 and arr[index-1][0]<=arr[i][1]):
      while(index!=0 and arr[index-1][0]<arr[i][1]):
        arr[index-1][1]=max(arr[index-1][1], arr[i][1])
        arr[index-1][0]=min(arr[index-1][0], arr[i][0])
        index-=1
    else:
      arr[index]=arr[i]
    index+=1
  for i in range(index):
    print("["+str(arr[i][0])+","+str(arr[i][1])+ "]")

mergeIntervals([[1,2],[3,5],[8,20],[45,60], [2,20]])