3Sum and 4Sum @ Python Leetcode

1) 3Sum

https://oj.leetcode.com/problems/3sum/

Given an array S of n integers, is there elements a, b, c in S such That a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.

Note:

• Elements in a triplet (a,b,C) must is in non-descending order. (ie, a ≤ b ≤ c)
• The solution set must not contain duplicate triplets.

    For example, given array S = {-1 0 1 2-1-4},    A solution set is:    ( -1, 0, 1)    (-1,-1, 2)

classSolution:#@return A list of lists of length 3, [[Val1,val2,val3]]    defthreesum (self, num): Num.sort () ans=[] Target=0 forIinchRange (0, Len (num)):if(I > 0 andNum[i] = = Num[i-1]):Continue  #Reserve first of all same valuesL, R = i + 1, len (num)-1 whileL <R:sum= Num[i] + num[l] +Num[r]ifsum = =target:ans.append ([Num[i], num[l], num[r]) whileL < R andNum[l] = = num[l + 1]: L = l + 1#Remove Duplicate                     whileL < R andNum[r] = = Num[r-1]: R = r-1#Remove DuplicateL, R = L + 1, r-1elifSum <target:l= L + 1Else: R= R-1returnAns

2) 4Sum

https://oj.leetcode.com/problems/4sum/

Given an array S of Nintegers, is there elements a,  b,  C, and Dinch Ssuch that a +  b +  C +  D= target? Find all unique quadruplets in the array which gives the sum of target.

Note:

• Elements in a quadruplet (a,b,c,D) must is in non-descending order. (ie, a ≤ b ≤ c ≤ d)
• The solution set must not contain duplicate quadruplets.

    For example, given array S = {1 0-1 0-2 2}, and target = 0.    A solution set is:    ( -1,  0, 0, 1)    ( -2,-1, 1, 2)    ( -2,  0, 0, 2)

classSolution:#@return A list of lists of length 4, [[Val1,val2,val3,val4]]    deffoursum (self, num, target): Num.sort () ans= []         forIinchRange (0, Len (num)):if(I > 0 andNum[i] = = Num[i-1]):Continue  #Reserve first of all same values             forJinchRange (i+1, Len (num)):if(J > i + 1 andNUM[J] = = Num[j-1]):Continue  #Reserve first of all same valuesL, R = j + 1, len (num)-1 whileL <R:sum= Num[i] + num[j] + num[l] +Num[r]ifsum = =target:ans.append ([Num[i], num[j], num[l], Num[r]]) whileL < R andNum[l] = = num[l + 1]: L = l + 1#Remove Duplicate                         whileL < R andNum[r] = = Num[r-1]: R = r-1#Remove DuplicateL, R = L + 1, r-1elifSum <target:l= L + 1Else: R= R-1returnAns

3Sum and 4Sum @ Python Leetcode