merge_intervals.py

def main(arr):
    arr.sort(key=lambda x: x[0])
    if arr:
        stack = [arr[0]]
    else:
        return []

    for start, end in arr[1:]:
        interval = stack[-1]
        if start > interval[1]:     # it's a new interval
            stack.append((start, end))
        else:
            stack[-1] = (interval[0], max(interval[1], end))  # it's an interval update

    return stack


if __name__ == "__main__":
    print(main([(1, 3), (2, 4), (5, 7), (6, 8), (10, 15)]))
    print(main([[6, 8], [1, 9], [2, 4], [4, 7]]))