tasks for today

1. 56.合并区间

2. 738.单调递增的数字

3. 968.监控二叉树（optional）

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class Solution:     def merge(self, intervals: List[List[int]]) -> List[List[int]]:         intervals.sort(key = lambda x: (x[0], x[1]))         result = []         sl, sr = intervals[0][0], intervals[0][1]         for i in intervals:             if i[0] > sr:                 result.append([sl,sr])                 sl, sr = i[0], i[1]             else:                 sl = min(sl, i[0])                 sr = max(sr, i[1])                  result.append([sl, sr])                  return result

2. 738.单调递增的数字

In this practice, the key mindset is: if the digits[i] < digits[i-1], the digits[i-1] will be deduct 1, and the all rest digits from i on should be changed to 9.

class Solution:     def monotoneIncreasingDigits(self, n: int) -> int:         if n == 0: return 0         digits = [int(i) for i in str(n)]         for i in range(len(digits) - 1, 0, -1):             if digits[i] < digits[i - 1]:                 digits[i - 1] -= 1                 for k in range(i, len(digits)):                     digits[k] = 9         result = 0         for i in digits:             result = 10*result + i          return result