18:四数之和

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

@@ -0,0 +1,116 @@
+//给你一个由 n 个整数组成的数组 nums ，和一个目标值 target 。请你找出并返回满足下述全部条件且不重复的四元组 [nums[a], nums[
+//b], nums[c], nums[d]] ： 
+//
+// 
+// 0 <= a, b, c, d < n 
+// a、b、c 和 d 互不相同 
+// nums[a] + nums[b] + nums[c] + nums[d] == target 
+// 
+//
+// 你可以按 任意顺序 返回答案 。 
+//
+// 
+//
+// 示例 1： 
+//
+// 
+//输入：nums = [1,0,-1,0,-2,2], target = 0
+//输出：[[-2,-1,1,2],[-2,0,0,2],[-1,0,0,1]]
+// 
+//
+// 示例 2： 
+//
+// 
+//输入：nums = [2,2,2,2,2], target = 8
+//输出：[[2,2,2,2]]
+// 
+//
+// 
+//
+// 提示： 
+//
+// 
+// 1 <= nums.length <= 200 
+// -10⁹ <= nums[i] <= 10⁹ 
+// -10⁹ <= target <= 10⁹ 
+// 
+// Related Topics 数组 双指针 排序 👍 976 👎 0
+
+package leetcode.editor.cn;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+//18:四数之和
+class FourSum {
+    public static void main(String[] args) {
+        //测试代码
+        Solution solution = new FourSum().new Solution();
+//        solution.fourSum(new int[]{1,0,-1,0,-2,2},0);
+        solution.fourSum(new int[]{0, 0, 0, 1000000000, 1000000000, 1000000000, 1000000000}, 1000000000);
+    }
+
+    //力扣代码
+    //leetcode submit region begin(Prohibit modification and deletion)
+    class Solution {
+        public List<List<Integer>> fourSum(int[] nums, int target) {
+            List<List<Integer>> result = new ArrayList<>();
+            if (nums == null || nums.length < 4) {
+                return result;
+            }
+            Arrays.sort(nums);
+            int length = nums.length;
+            long sum;
+            for (int i = 0; i < length - 3; i++) {
+                if (i > 0 && nums[i] == nums[i - 1]) {
+                    continue;
+                }
+                sum = (long)nums[i] + nums[i + 1] + nums[i + 2] + nums[i + 3];
+                if (sum > target) {
+                    break;
+                }
+                sum = (long)nums[i] + nums[length - 3] + nums[length - 2] + nums[length - 1];
+                if (sum < target) {
+                    continue;
+                }
+                for (int j = i + 1; j < length - 2; j++) {
+                    if (j > i + 1 && nums[j] == nums[j - 1]) {
+                        continue;
+                    }
+                    sum = (long)nums[i] + nums[j] + nums[j + 1] + nums[j + 2];
+                    if (sum > target) {
+                        break;
+                    }
+                    sum = (long)nums[i] + nums[j] + nums[length - 2] + nums[length - 1];
+                    if (sum < target) {
+                        continue;
+                    }
+                    int start = j + 1;
+                    int end = length - 1;
+                    while (start < end) {
+                        sum = (long)nums[i] + nums[j] + nums[start] + nums[end];
+                        if (sum == target) {
+                            result.add(Arrays.asList(nums[i], nums[j], nums[start], nums[end]));
+                            while (start < end && nums[start] == nums[start + 1]) {
+                                start++;
+                            }
+                            start++;
+                            while (start < end && nums[end] == nums[end - 1]) {
+                                end--;
+                            }
+                            end--;
+                        } else if (sum < target) {
+                            start++;
+                        } else {
+                            end--;
+                        }
+                    }
+                }
+            }
+            return result;
+        }
+    }
+//leetcode submit region end(Prohibit modification and deletion)
+
+}

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

@@ -51,7 +51,9 @@ public class MergeSortedArray {
     //leetcode submit region begin(Prohibit modification and deletion)
     class Solution {
         public void merge(int[] nums1, int m, int[] nums2, int n) {
-            if (m + n - m >= 0) System.arraycopy(nums2, 0, nums1, m, m + n - m);
+            if (m + n - m >= 0) {
+                System.arraycopy(nums2, 0, nums1, m, m + n - m);
+            }
             Arrays.sort(nums1);
         }
     }

src/main/java/leetcode/editor/cn/doc/content/FourSum.md

@@ -0,0 +1,36 @@
+<p>给你一个由 <code>n</code> 个整数组成的数组&nbsp;<code>nums</code> ，和一个目标值 <code>target</code> 。请你找出并返回满足下述全部条件且不重复的四元组&nbsp;<code>[nums[a], nums[b], nums[c], nums[d]]</code> ：</p>
+
+<ul>
+	<li><code>0 &lt;= a, b, c, d&nbsp;&lt; n</code></li>
+	<li><code>a</code>、<code>b</code>、<code>c</code> 和 <code>d</code> <strong>互不相同</strong></li>
+	<li><code>nums[a] + nums[b] + nums[c] + nums[d] == target</code></li>
+</ul>
+
+<p>你可以按 <strong>任意顺序</strong> 返回答案 。</p>
+
+<p>&nbsp;</p>
+
+<p><strong>示例 1：</strong></p>
+
+<pre>
+<strong>输入：</strong>nums = [1,0,-1,0,-2,2], target = 0
+<strong>输出：</strong>[[-2,-1,1,2],[-2,0,0,2],[-1,0,0,1]]
+</pre>
+
+<p><strong>示例 2：</strong></p>
+
+<pre>
+<strong>输入：</strong>nums = [2,2,2,2,2], target = 8
+<strong>输出：</strong>[[2,2,2,2]]
+</pre>
+
+<p>&nbsp;</p>
+
+<p><strong>提示：</strong></p>
+
+<ul>
+	<li><code>1 &lt;= nums.length &lt;= 200</code></li>
+	<li><code>-10<sup>9</sup> &lt;= nums[i] &lt;= 10<sup>9</sup></code></li>
+	<li><code>-10<sup>9</sup> &lt;= target &lt;= 10<sup>9</sup></code></li>
+</ul>
+<div><div>Related Topics</div><div><li>数组</li><li>双指针</li><li>排序</li></div></div><br><div><li>👍 976</li><li>👎 0</li></div>