dp 最大递增子序列问题。

  1. 先对 letters 进行排序
  2. 初始化 dp, dp[0] = 1
  3. dp[i] = max(dp[j] + 1, dp[i]) j < i and letters[i][0] > letters[j][0] and letters[i][1] > letters[j][1]
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# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
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# @param letters int整型二维数组 
# @return int整型
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class Solution:
    def maxLetters(self , letters: List[List[int]]) -> int:
        # write code here
        letters.sort()
        n = len(letters)
        dp = [1 for _ in range(n)]
        for i in range(1, n):
            for j in range(i):
                if letters[i][0] > letters[j][0] and letters[i][1] > letters[j][1]:
                    dp[i] = max(dp[i], dp[j] + 1)
        return max(dp)