solve 18

Author: Zhang Xiaodong

src/solution/mod.rs

@@ -13,3 +13,4 @@ mod s0014_longest_common_prefix;
 mod s0015_3sum;
 mod s0016_3sum_closest;
 mod s0017_letter_combinations_of_a_phone_number;
+mod s0018_4sum;

src/solution/s0018_4sum.rs

@@ -0,0 +1,117 @@
+/**
+ * [18] 四数之和
+ *
+ * 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]] （若两个四元组元素一一对应，则认为两个四元组重复）：
+ *
+ * 	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
+ * 	-10^9 <= nums[i] <= 10^9
+ * 	-10^9 <= target <= 10^9
+ *
+ */
+pub struct Solution {}
+
+// problem: https://leetcode.cn/problems/4sum/
+// discuss: https://leetcode.cn/problems/4sum/discuss/?currentPage=1&orderBy=most_votes&query=
+
+// submission codes start here
+
+impl Solution {
+    pub fn four_sum(nums: Vec<i32>, target: i32) -> Vec<Vec<i32>> {
+        if nums.len() < 4 {
+            return vec![];
+        }
+        let mut nums = nums;
+        nums.sort();
+
+        let mut res: Vec<Vec<i32>> = vec![];
+
+        let target = target as i64;
+        let mut i = 0;
+        while i < nums.len() - 3 {
+            let mut j = i + 1;
+            while j < nums.len() - 2 {
+                let mut k = j + 1;
+                let mut l = nums.len() - 1;
+                while k < l {
+                    let curr: i64 = nums[i] as i64 + nums[j] as i64 + nums[k] as i64 + nums[l] as i64;
+                    if curr == target {
+                        res.push(vec![nums[i], nums[j], nums[k], nums[l]]);
+                        k = Self::find_next_uniq(&nums, k, true);
+                        l = Self::find_next_uniq(&nums, l, false);
+                    } else if curr > target {
+                        l = Self::find_next_uniq(&nums, l, false);
+                    } else {
+                        k = Self::find_next_uniq(&nums, k, true);
+                    }
+                }
+                j = Self::find_next_uniq(&nums, j, true);
+            }
+            i = Self::find_next_uniq(&nums, i, true);
+        }
+
+        res
+    }
+
+    #[inline(always)]
+    fn find_next_uniq(nums: &[i32], idx: usize, forward: bool) -> usize {
+        let curr = nums[idx];
+        let mut i = idx;
+        if forward {
+            while i < nums.len() && nums[i] == curr {
+                i += 1;
+            }
+        } else {
+            while i > 0 && nums[i] == curr {
+                i -= 1;
+            }
+        }
+        i
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use std::vec;
+
+    use super::*;
+
+    #[test]
+    fn test_18() {
+        assert_eq!(
+            Solution::four_sum(vec![1, 0, -1, 0, -2, 2], 0),
+            vec![vec![-2, -1, 1, 2], vec![-2, 0, 0, 2], vec![-1, 0, 0, 1]]
+        );
+
+        assert_eq!(
+            Solution::four_sum(vec![2, 2, 2, 2, 2], 8),
+            vec![vec![2, 2, 2, 2]]
+        );
+
+        let emptyvec: Vec<Vec<i32>> = vec![];
+        assert_eq!(
+            Solution::four_sum(vec![1000000000, 1000000000, 1000000000, 1000000000], -294967296),
+            emptyvec
+        );
+    }
+}