56-merge-intervals.py
problem: ---
problem:

Given a collection of intervals, merge all overlapping intervals.

Example 1:

Input: [[1,3],[2,6],[8,10],[15,18]]
Output: [[1,6],[8,10],[15,18]]
Explanation: Since intervals [1,3] and [2,6] overlaps, merge them into [1,6].

Example 2:
Input: [[1,4],[4,5]]
Output: [[1,5]]
Explanation: Intervals [1,4] and [4,5] are considered overlapping.
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bug_fixes: ---
bug_fixes:
Replace `intervals = intervals.sort(key=lambda x: x[0])` with `intervals.sort(key=lambda x: x[0])` on line 3.
Replace `range(intervals)` with `intervals` on line 5.
Add `return merged` on line 9.
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bug_desc: ---
bug_desc:
On line 3, intervals is sorted and the result is set to `intervals`. This is incorrect as the sort method works in-place and does not return anything. This is a syntactical mistake and can be fixed by simply writing `intervals.sort(key=lambda x: x[0])`.
On line 5, the range function is used incorrectly since the array intervals is passed into the function. This is a syntactical mistake and should be changed to `for interval in intervals` to iterate over the subarrays in intervals correctly.
On line 9, or after line 8, nothing is returned from the method, which is incorrect behavior. This can be fixed by returning the array `merged`.
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line_no: ---
line_no:
3
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buggy_code: ---
buggy_code:
1. class Solution:
2.     def merge(self, intervals: List[List[int]]) -> List[List[int]]:
3.       intervals = intervals.sort(key=lambda x: x[0])
4.       merged = []
5.       for interval in range(intervals):
6.         if not merged or merged[-1][1] < interval[0]:
7.           merged.append(interval)
8.         else:
9.           merged[-1][1] = max(merged[-1][1], interval[1])
10.       
11. 
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correct_code: ---
correct_code:
1. class Solution:
2.     def merge(self, intervals: List[List[int]]) -> List[List[int]]:
3.       intervals.sort(key=lambda x: x[0])
4.       merged = []
5.       for interval in intervals:
6.         if not merged or merged[-1][1] < interval[0]:
7.           merged.append(interval)
8.         else:
9.           merged[-1][1] = max(merged[-1][1], interval[1])
10.       return merged
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