Added Find the Index of the First Occurrence in a String

Author: ryanoneill

src/find_the_index_of_the_first_occurrence_in_a_string.rs

@@ -0,0 +1,77 @@
+/// Given two strings `needle` and `haystack`, return the index of the first
+/// occurrence of `needle` in `haystack`, or `-1` if `needle` is not part of
+/// `haystack`.
+struct Solution;
+
+impl Solution {
+
+    pub fn str_str(haystack: String, needle: String) -> i32 {
+        let mut result = -1;
+
+        let h: Vec<char> = haystack.chars().collect();
+        let n: Vec<char> = needle.chars().collect();
+
+        let hlen = h.len();
+        let nlen = n.len();
+
+        for i in 0..hlen {
+            let mut index = 0;
+            while (index < nlen) && (i + index < hlen) && h[i+index] == n[index] {
+                index += 1;
+            }
+            if index == nlen {
+                result = i as i32;
+                break;
+            }
+        }
+
+        result
+    }
+
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Solution;
+
+    #[test]
+    fn example_1() {
+        let haystack = "sadbutsad".to_string();
+        let needle = "sad".to_string();
+        let result = Solution::str_str(haystack, needle);
+        assert_eq!(result, 0);
+    }
+
+    #[test]
+    fn example_2() {
+        let haystack = "leetcode".to_string();
+        let needle = "leeto".to_string();
+        let result = Solution::str_str(haystack, needle);
+        assert_eq!(result, -1);
+    }
+
+    #[test]
+    fn middle() {
+        let haystack = "goodbye".to_string();
+        let needle = "od".to_string();
+        let result = Solution::str_str(haystack, needle);
+        assert_eq!(result, 2);
+    }
+
+    #[test]
+    fn end() {
+        let haystack = "cartoon".to_string();
+        let needle = "toon".to_string();
+        let result = Solution::str_str(haystack, needle);
+        assert_eq!(result, 3);
+    }
+
+    #[test]
+    fn off_end() {
+        let haystack = "national".to_string();
+        let needle = "ale".to_string();
+        let result = Solution::str_str(haystack, needle);
+        assert_eq!(result, -1);
+    }
+
+}