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3 Longest Substring Without Repeating Characters
11 Container With Most Water
15 3Sum
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42 Trapping Rain Water
76 Minimum Window Substring
80 Remove Duplicates from Sorted Array II
88 Merge Sorted Array
125 Valid Palindrome
159 Longest Substring with At Most Two Distinct Characters
167 Two Sum II - Input array is sorted
202 Happy Number
209 Minimum Size Subarray Sum
259 3Sum Smaller
283 Move Zeroes
340 Longest Substring with At Most K Distinct Characters
344 Reverse String
345 Reverse Vowels of a String
349 Intersection of Two Arrays
350 Intersection of Two Arrays II
360 Sort Transformed Array
395 Longest Substring with At Least K Repeating Characters
424 Longest Repeating Character Replacement
438 Find All Anagrams in a String
487 Max Consecutive Ones II
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15 3Sum

15. 3Sum​

1. Question

Given an arraySofnintegers, are there elementsa,b,cinSsuch thata+b+c= 0? Find all unique triplets in the array which gives the sum of zero.
Note:The solution set must not contain duplicate triplets.
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For example, given array S = [-1, 0, 1, 2, -1, -4],
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​
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A solution set is:
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[
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[-1, 0, 1],
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[-1, -1, 2]
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]
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2. Implementation

(1) Two Pointers
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class Solution {
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public List<List<Integer>> threeSum(int[] nums) {
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List<List<Integer>> res = new ArrayList<>();
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Arrays.sort(nums);
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​
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for (int i = 0; i < nums.length - 2; i++) {
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if (i > 0 && nums[i - 1] == nums[i]) {
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continue;
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}
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​
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int j = i + 1, k = nums.length - 1;
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​
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while (j < k) {
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int sum = nums[i] + nums[j] + nums[k];
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​
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if (sum == 0) {
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res.add(Arrays.asList(nums[i], nums[j], nums[k]));
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++j;
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--k;
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​
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while (j < k && nums[j - 1] == nums[j]) ++j;
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while (j < k && nums[k] == nums[k + 1]) --k;
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}
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else if (sum < 0) {
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++j;
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}
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else {
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--k;
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}
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}
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}
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return res;
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}
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}
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3. Time & Space Complexity

Two Pointers: 时间复杂度O(n^2)
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Contents
15. 3Sum
1. Question
2. Implementation
3. Time & Space Complexity