diff --git a/src/bin/15_3sum.rs b/src/bin/15_3sum.rs
index f5c0f2b..5494883 100644
--- a/src/bin/15_3sum.rs
+++ b/src/bin/15_3sum.rs
@@ -1,26 +1,32 @@
 fn main() {
     println!("{:?}", three_sum(vec![-1,0,1,2,-1,-4]));
+    println!("{:?}", three_sum(vec![0,0,0,0,0,0]));
+    println!("{:?}", three_sum(vec![-2,0,0,2,2]));
 }
 
 // TODO: fix and optimize
 pub fn three_sum(mut nums: Vec<i32>) -> Vec<Vec<i32>> {
-    let mut result: Vec<Vec<i32>> = Vec::new();
-    let mut seen = std::collections::HashSet::<i32>::with_capacity(nums.len());
-    let mut seen2 = std::collections::HashSet::<i32>::with_capacity(nums.len()-1);
+    let mut result = Vec::<Vec<i32>>::new();
     nums.sort();
     for i in 0..nums.len()-2 {
-        if seen.contains(&nums[i]) { continue; }
-        for j in i+1..nums.len()-1 {
-            if seen2.contains(&nums[j]) { continue; }
-            for k in j+1..nums.len() {
-                if nums[i] + nums[j] + nums[k] == 0 {
+        if i > 0 && nums[i] == nums[i - 1] { continue; }
+        let (mut j, mut k) = (i + 1, nums.len() - 1);
+        while j < k {
+            if j > i + 1 && nums[j - 1] == nums[j] {
+                j += 1; continue;
+            }
+            if k < nums.len() - 1 && nums[k + 1] == nums[k] {
+                k -= 1; continue;
+            }
+            match (nums[i] + nums[j] + nums[k]).cmp(&0) {
+                std::cmp::Ordering::Less => { j += 1; },
+                std::cmp::Ordering::Greater => { k -= 1 },
+                std::cmp::Ordering::Equal => {
                     result.push(vec![nums[i], nums[j], nums[k]]);
+                    j += 1; k -= 1;
                 }
             }
-            seen2.insert(nums[j]);
         }
-        seen.insert(nums[i]);
-        seen2.clear();
     }
     return result;
 }