Added First Unique Character in a String

Author: ryanoneill

src/first_unique_character_in_a_string.rs

@@ -0,0 +1,61 @@
+use std::collections::HashMap;
+use std::collections::HashSet;
+
+/// Given a string `s`, find the first non-repeating character in it and return
+/// its index. If it does not exist, return `-1`.
+struct Solution;
+
+impl Solution {
+
+    fn to_counts(s: &str) -> HashMap<char, usize> {
+        let mut result = HashMap::new();
+        for c in s.chars() {
+            result.entry(c)
+                .and_modify(|count| { *count += 1; })
+                .or_insert(1);
+        }
+        result
+    }
+
+    pub fn first_uniq_char(s: String) -> i32 {
+        let counts = Self::to_counts(&s);
+
+        let mut result = -1;
+        for (i, c) in s.chars().enumerate() {
+            if counts[&c] == 1 {
+                result = i as i32;
+                break;
+            }
+        }
+
+        result
+    }
+
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Solution;
+
+    #[test]
+    fn example_1() {
+        let s = "leetcode".to_string();
+        let result = Solution::first_uniq_char(s);
+        assert_eq!(result, 0);
+    }
+
+    #[test]
+    fn example_2() {
+        let s = "loveleetcode".to_string();
+        let result = Solution::first_uniq_char(s);
+        assert_eq!(result, 2);
+    }
+
+    #[test]
+    fn example_3() {
+        let s = "aabb".to_string();
+        let result = Solution::first_uniq_char(s);
+        assert_eq!(result, -1);
+    }
+
+}

src/lib.rs

@@ -30,6 +30,7 @@ pub mod swap_nodes_in_pairs; // 24
 
 pub mod remove_duplicates_from_sorted_array; // 26
 pub mod remove_element; // 27
+pub mod find_the_index_of_the_first_occurrence_in_a_string; // 28
 
 pub mod range_sum_query_immutable; // 30
 
@@ -118,6 +119,8 @@ pub mod kth_smallest_element_in_a_sorted_matrix; // 378
 
 pub mod ransom_note; // 383
 
+pub mod first_unique_character_in_a_string;
+
 pub mod is_subsequence; // 392
 
 pub mod fizz_buzz; // 412