15_三数之和.py

# -*- coding: utf-8 -*-
"""
Created on Fri Jun 12 09:30:27 2020

@author: leiya
"""

#sort+三指针
#一个指针从头开始，另外两个指针一左一右夹逼寻找，这也是sort的意义
class Solution:
    def threeSum(self, nums: List[int]) -> List[List[int]]:
        n = len(nums)
        res=[]
        if(not nums or n<3):
            return []
        nums.sort()
        res=[]
        for i in range(n-2):
            if(nums[i]>0):
                return res
            if(i>0 and nums[i]==nums[i-1]):
                continue
            L=i+1
            R=n-1
            while(L<R):
                if(nums[i]+nums[L]+nums[R]==0):
                    res.append([nums[i],nums[L],nums[R]])
                    while(L<R and nums[L]==nums[L+1]):
                        L=L+1
                    while(L<R and nums[R]==nums[R-1]):
                        R=R-1
                    L=L+1
                    R=R-1
                elif(nums[i]+nums[L]+nums[R]>0):
                    R=R-1
                else:
                    L=L+1
        return res