• ## Algorithm related problems

Time：2021-3-3

1. Permutation problem You need to use Python’s itertools module import itertools a=[1,2,3] #Take, arrange (mathematical formula: A32) for i in itertools.permutations (a, 2): # 2 is taken twice. A can be a string or a list print(i) ”’ (1, 2) (1, 3) (2, 1) (2, 3) (3, 1) (3, 2) ”’ #Combination (mathematical formula: […]

• ## leetcode454. 4Sum II

Time：2020-6-16

Title Requirements Given four lists A, B, C, D of integer values, compute how many tuples`(i, j, k, l)`there are such that`A[i] + B[j] + C[k] + D[l]`is zero. To make problem a bit easier, all A, B, C, D have same length of N where 0 ≤ N ≤ 500. All integers are in […]

• ## LeetCode 18. 4 Sum

Time：2020-3-23

Title Description (medium difficulty) Similar to 3sum, it’s just to find four numbers so that the sum is target and there can’t be duplicate sequences. If you haven’t done 3sum before, you can take a look at it first. You just added a cycle on the basis of the above. public List<List<Integer>> fourSum(int[] num, int […]