N数之和

import org.graalvm.compiler.nodes.KillingBeginNode;
import org.graalvm.compiler.nodes.calc.LeftShiftNode;

import java.sql.Array;
import java.util.ArrayList;
import java.util.Arrays;

/**
 * <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<strong>不重复</strong>的四元组&nbsp;<code>[nums[a], nums[b], nums[c], nums[d]]</code>&nbsp;（若两个四元组元素一一对应，则认为两个四元组重复）：</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>👍 1320</li><li>👎 0</li></div>
 */

//leetcode submit region begin(Prohibit modification and deletion)
class Solution {
    public List<List<Integer>> fourSum(int[] nums, int target) {
        Arrays.sort(nums);
        return nSumTarget(nums,4,0,target);
    }

    public List<List<Integer>> nSumTarget(int[] nums, int n, int start, long                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         target) {
        List<List<Integer>> res = new ArrayList<>();
        int sz = nums.length;
        if (n < 2 || sz < n) return res;

        if (n == 2) {
            int left = start, right = nums.length - 1;
            while (left < right) {
                int sum = nums[left] + nums[right];
                int low = nums[left];
                int high = nums[right];
                if (sum > target)
                    while (left < right && nums[right] == high) right--;
                else if (sum < target)
                    while (left < right && nums[left] == low) left++;
                else {
                    res.add(Arrays.asList(nums[left], nums[right]));
                    while (left < right && nums[right] == high) right--;
                    while (left < right && nums[left] == low) left++;
                }
            }
        } else {
            for (int i = start; i < nums.length; i++) {
                int num = nums[i];
                List<List<Integer>> twoSum = nSumTarget(nums, n - 1, i + 1, target - num);
                for (int j = 0; j < twoSum.size(); j++) {
                    List<Integer> temp = new ArrayList<>();
                    temp.add(nums[i]);
                    temp.addAll(twoSum.get(j));
                    res.add(temp);
                }
                while (i < nums.length - 1 && num == nums[i + 1]) {
                    i++;
                }
            }
        }
        return res;
    }
}


//leetcode submit region end(Prohibit modification and deletion)