Add longest_substring_with_unique_chars_optimized

Author: marttp

rust/Sliding Windows/longest_substring_with_unique_chars_optimized.rs

@@ -0,0 +1,30 @@
+fn longest_substring_with_unique_chars_optimized(s: String) -> i32 {
+    use std::collections::HashMap;
+
+    let mut max_len = 0;
+    let mut prev_indexes = HashMap::new();
+    let mut left = 0;
+    let mut right = 0;
+    // Shadowing 's' by converting it to a byte array/slice.
+    let s = s.as_bytes();
+
+    while right < s.len() {
+        // If a previous index of the current character is present
+        // in the current window, it's a duplicate character in the
+        // window. 
+        if let Some(&prev_index) = prev_indexes.get(&s[right]) {
+            // Shrink the window to exclude the previous occurrence
+            // of this character.
+            if prev_index >= left {
+                left = prev_index + 1;
+            }
+        }
+        // Update 'max_len' if the current window is larger.
+        max_len = max_len.max(right - left + 1);
+        prev_indexes.insert(s[right], right);
+        // Expand the window.
+        right += 1;
+    }
+
+    max_len as i32
+}