15:三数之和

src/main/java/leetcode/editor/cn/ThreeSum.java

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+//给你一个包含 n 个整数的数组 nums，判断 nums 中是否存在三个元素 a，b，c ，使得 a + b + c = 0 ？请你找出所有和为 0 且不重
+//复的三元组。 
+//
+// 注意：答案中不可以包含重复的三元组。 
+//
+// 
+//
+// 示例 1： 
+//
+// 
+//输入：nums = [-1,0,1,2,-1,-4]
+//输出：[[-1,-1,2],[-1,0,1]]
+// 
+//
+// 示例 2： 
+//
+// 
+//输入：nums = []
+//输出：[]
+// 
+//
+// 示例 3： 
+//
+// 
+//输入：nums = [0]
+//输出：[]
+// 
+//
+// 
+//
+// 提示： 
+//
+// 
+// 0 <= nums.length <= 3000 
+// -105 <= nums[i] <= 105 
+// 
+// Related Topics 数组 双指针 
+// 👍 3303 👎 0
+
+package leetcode.editor.cn;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import java.util.stream.Collectors;
+
+//15:三数之和
+public class ThreeSum {
+    public static void main(String[] args) {
+        //测试代码
+        Solution solution = new ThreeSum().new Solution();
+//        solution.threeSum(new int[]{-1, 0, 1, 2, -1, -4});
+//        solution.threeSum(new int[]{-4, -2, -2, -2, 0, 1, 2, 2, 2, 3, 3, 4, 4, 6, 6});
+        solution.threeSum(new int[]{-4, -2, -1});
+    }
+
+    //力扣代码
+    //leetcode submit region begin(Prohibit modification and deletion)
+    class Solution {
+        public List<List<Integer>> threeSum(int[] nums) {
+            int n = nums.length;
+            Arrays.sort(nums);
+            List<List<Integer>> ans = new ArrayList<List<Integer>>();
+            for (int first = 0; first < n; ++first) {
+                if (first > 0 && nums[first] == nums[first - 1]) {
+                    continue;
+                }
+                int third = n - 1;
+                int target = -nums[first];
+                for (int second = first + 1; second < n; ++second) {
+                    if (second > first + 1 && nums[second] == nums[second - 1]) {
+                        continue;
+                    }
+                    while (second < third && nums[second] + nums[third] > target) {
+                        --third;
+                    }
+                    if (second == third) {
+                        break;
+                    }
+                    if (nums[second] + nums[third] == target) {
+                        List<Integer> list = new ArrayList<Integer>();
+                        list.add(nums[first]);
+                        list.add(nums[second]);
+                        list.add(nums[third]);
+                        ans.add(list);
+                    }
+                }
+            }
+            return ans;
+        }
+    }
+//leetcode submit region end(Prohibit modification and deletion)
+
+}

src/main/java/leetcode/editor/cn/ThreeSum.md

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+<p>给你一个包含 <code>n</code> 个整数的数组 <code>nums</code>，判断 <code>nums</code> 中是否存在三个元素 <em>a，b，c ，</em>使得 <em>a + b + c = </em>0 ？请你找出所有和为 <code>0</code> 且不重复的三元组。</p>
+
+<p><strong>注意：</strong>答案中不可以包含重复的三元组。</p>
+
+<p> </p>
+
+<p><strong>示例 1：</strong></p>
+
+<pre>
+<strong>输入：</strong>nums = [-1,0,1,2,-1,-4]
+<strong>输出：</strong>[[-1,-1,2],[-1,0,1]]
+</pre>
+
+<p><strong>示例 2：</strong></p>
+
+<pre>
+<strong>输入：</strong>nums = []
+<strong>输出：</strong>[]
+</pre>
+
+<p><strong>示例 3：</strong></p>
+
+<pre>
+<strong>输入：</strong>nums = [0]
+<strong>输出：</strong>[]
+</pre>
+
+<p> </p>
+
+<p><strong>提示：</strong></p>
+
+<ul>
+	<li><code>0 <= nums.length <= 3000</code></li>
+	<li><code>-10<sup>5</sup> <= nums[i] <= 10<sup>5</sup></code></li>
+</ul>
+<div><div>Related Topics</div><div><li>数组</li><li>双指针</li></div></div>\n<div><li>👍 3303</li><li>👎 0</li></div>