Added solution for 389

Author: chirag64

00389. Find the Difference389. Find the Difference.rs

@@ -0,0 +1,20 @@
+use std::collections::HashMap;
+
+impl Solution {
+    // Count instances of each character in s in a hashmap. Then subtract those instances from the same hashmap while iterating through t. If any character does not exist in hashmap or is left 0 times while iterating t, it means that is the extra character added in t
+    pub fn find_the_difference(s: String, t: String) -> char {
+        let mut map = HashMap::new();
+        for ch in s.chars() {
+            let count = map.entry(ch).or_insert(0);
+            *count += 1;
+        }
+        for ch in t.chars() {
+            let count = map.entry(ch).or_insert(0);
+            if *count == 0 {
+                return ch;
+            }
+            *count -= 1;
+        }
+        return '0';
+    }
+}