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package class25;
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import java.util.ArrayList;
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import java.util.Arrays;
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import java.util.List;
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// 本题测试链接 : https://leetcode.com/problems/3sum/
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public class Code02_3Sum {
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public static List<List<Integer>> threeSum(int[] nums) {
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Arrays.sort(nums);
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int N = nums.length;
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List<List<Integer>> ans = new ArrayList<>();
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for (int i = N - 1; i > 1; i--) { // 三元组最后一个数,是arr[i] 之前....二元组 + arr[i]
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if (i == N - 1 || nums[i] != nums[i + 1]) {
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List<List<Integer>> nexts = twoSum(nums, i - 1, -nums[i]);
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for (List<Integer> cur : nexts) {
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cur.add(nums[i]);
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ans.add(cur);
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}
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}
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}
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return ans;
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}
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// nums[0...end]这个范围上,有多少个不同二元组,相加==target,全返回
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// {-1,5} K = 4
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// {1, 3}
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public static List<List<Integer>> twoSum(int[] nums, int end, int target) {
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int L = 0;
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int R = end;
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List<List<Integer>> ans = new ArrayList<>();
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while (L < R) {
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if (nums[L] + nums[R] > target) {
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R--;
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} else if (nums[L] + nums[R] < target) {
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L++;
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} else { // nums[L] + nums[R] == target
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if (L == 0 || nums[L - 1] != nums[L]) {
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List<Integer> cur = new ArrayList<>();
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cur.add(nums[L]);
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cur.add(nums[R]);
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ans.add(cur);
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}
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L++;
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}
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}
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return ans;
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}
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public static int findPairs(int[] nums, int k) {
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Arrays.sort(nums);
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int left = 0, right = 1;
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int result = 0;
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while (left < nums.length && right < nums.length) {
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if (left == right || nums[right] - nums[left] < k) {
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right++;
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} else if (nums[right] - nums[left] > k) {
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left++;
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} else {
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left++;
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result++;
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while (left < nums.length && nums[left] == nums[left - 1])
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left++;
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}
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}
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return result;
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}
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}
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