3sum (#2675)

Author: DaleSeo

3sum/DaleSeo.rs

@@ -0,0 +1,37 @@
+// TC: O(n^2)
+// SC: O(1)
+impl Solution {
+    pub fn three_sum(mut nums: Vec<i32>) -> Vec<Vec<i32>> {
+        nums.sort_unstable();
+        let n = nums.len();
+        let mut triplets = Vec::new();
+
+        for i in 0..n {
+            if i > 0 && nums[i] == nums[i - 1] {
+                continue;
+            }
+
+            let (mut low, mut high) = (i + 1, n - 1);
+            while low < high {
+                let three_sum = nums[i] + nums[low] + nums[high];
+                if three_sum < 0 {
+                    low += 1;
+                } else if three_sum > 0 {
+                    high -= 1;
+                } else {
+                    triplets.push(vec![nums[i], nums[low], nums[high]]);
+                    low += 1;
+                    high -= 1;
+                    while low < high && nums[low] == nums[low - 1] {
+                        low += 1;
+                    }
+                    while low < high && nums[high] == nums[high + 1] {
+                        high -= 1;
+                    }
+                }
+            }
+        }
+
+        triplets
+    }
+}