Implemented p16, minor optimization in p15

src/p15_3sum.rs

@@ -13,13 +13,14 @@ impl Solution {
                 if k < nums.len() - 1 && nums[k + 1] == nums[k] {
                     k -= 1; continue;
                 }
-                match (nums[i] + nums[j] + nums[k]).cmp(&0) {
+                match (nums[i] + nums[j] + nums[k]).signum() {
-                    std::cmp::Ordering::Less => { j += 1; },
+                    -1 => { j += 1; },
-                    std::cmp::Ordering::Greater => { k -= 1 },
+                    1 => { k -= 1 },
-                    std::cmp::Ordering::Equal => {
+                    0 => {
                         result.push(vec![nums[i], nums[j], nums[k]]);
                         j += 1; k -= 1;
-                    }
+                    },
+                    _ => ()
                 }
             }
         }

src/p16_3sum_closest.rs

@@ -1,8 +1,24 @@
 pub struct Solution;
 impl Solution {
-    pub fn three_sum_closest(nums: Vec<i32>, target: i32) -> i32 {
+    pub fn three_sum_closest(mut nums: Vec<i32>, target: i32) -> i32 {
-        
+        let mut delta = i32::MAX / 2;
-        return 0;
+        nums.sort();
+        for i in 0..nums.len()-2 {
+            if i > 0 && nums[i] == nums[i - 1] { continue; }
+            let (mut j, mut k) = (i + 1, nums.len() - 1);
+            while j < k {
+                let sum = nums[i] + nums[j] + nums[k];
+                let new_delta = sum - target;
+                match new_delta.signum() {
+                    -1 => { j += 1; },
+                    1 => { k -= 1 },
+                    0 => { return target; },
+                    _ => ()
+                }
+                if new_delta.abs() < delta.abs() { delta = new_delta; }
+            }
+        }
+        return target + delta;
     }
 }