max number of k-sum pairs

max_k_sum_pairs/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "max_k_sum_pairs"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

max_k_sum_pairs/src/main.rs

@@ -0,0 +1,39 @@
+fn main() {
+    let mut nums = [1, 2, 3, 4];
+    dbg!(foo(&mut nums, 5));
+    let mut nums = [3, 1, 3, 4, 3];
+    dbg!(foo(&mut nums, 6));
+}
+
+fn foo(nums: &mut [i32], k: i32) -> i32 {
+    let mut max = 0;
+    nums.sort_unstable();
+
+    let mut left = 0;
+    let mut right = nums.len() - 1;
+
+    while left < right {
+        let lv = nums[left];
+        let rv = nums[right];
+        let sum = lv + rv;
+        if sum < k {
+            if lv < rv {
+                left += 1;
+            } else {
+                right -= 1;
+            }
+        } else if sum > k {
+            if rv > lv {
+                right -= 1;
+            } else {
+                left += 1;
+            }
+        } else {
+            max += 1;
+            left += 1;
+            right -= 1;
+        }
+    }
+
+    max
+}