Leetcode 16-18

No. 16 3Sum Closest (EASY PASS)

Solution: Two Pointers

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No. 17 Letter Combinations of a Phone Number

 

 Solution: Recursion 从后往前

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No. 18 4Sum

Solution:

方法一：跟2Sum题目一样，构建Hash Tale，将两个数字相加成为key，value存储两个数字的index（以tuple形式(i, j)）。