Added solution for 1748

Author: chirag64

01748. Sum of Unique Elements.rs

@@ -0,0 +1,25 @@
+use std::collections::HashMap;
+
+impl Solution {
+    // Keep count of instances of each number inside the vector. If it is counted first time, add it to the sum. If it is counted a second time, subtract it back from the sum since it need not be counted and it was added earlier. For all subsequent times a number is counted, keep counting it but ignore it from the sum
+    pub fn sum_of_unique(nums: Vec<i32>) -> i32 {
+        let mut sum = 0;
+        
+        // Count instances of each element
+        let mut map = HashMap::new();
+        for num in &nums {
+            let count = map.entry(num).or_insert(0);
+            *count += 1;
+            
+            if *count == 1 {
+                sum += num;
+            }
+            
+            if *count == 2 {
+                sum -= num;
+            }
+        }
+        
+        return sum;
+    }
+}