Rust challenge 2 (YearOfProgramming#416)

* Add main.rs to use find_single mod

* Add test cases

* Add print statements for more clarity

* Add README.md

challenge_2/rust/makernaren/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "makernaren"
+version = "0.1.0"
+authors = ["naren <makernaren@gmail.com>"]
+
+[dependencies]

challenge_2/rust/makernaren/README.md

@@ -0,0 +1,18 @@
+## Single Number
+#### To run the code : 
+* Open this directory in terminal and run `cargo run` to compile and run the code.
+* To test the code just run, `cargo test` in same directory.
+```
+$ cargo run
+    Finished debug [unoptimized + debuginfo] target(s) in 0.62 secs
+     Running `target/debug/makernaren`
+Given array is [1, 1, 2, 2, 3, 3, 5] 
+Single occurance : 5
+
+$ cargo test
+    Finished debug [unoptimized + debuginfo] target(s) in 0.70 secs
+     Running target/debug/makernaren-bf4fafb462d1be5f
+running 1 test
+test single_number::tests::test_int ... ok
+
+test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured

challenge_2/rust/makernaren/src/main.rs

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+mod single_number;
+fn main() {
+    // let input = vec!['a', 'a', 'b', 'b', 'c', 'c', 'd'];
+   	let input = vec![1, 1, 2, 2, 3, 3, 5];
+    println!("Given array is {:?} \n Single occurance : {}",input.clone(), single_number::find_single(input));
+
+}

challenge_2/rust/makernaren/src/single_number.rs

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+use std::collections::HashMap;
+
+// Finds the unique character in given array
+pub fn find_single(input: Vec<i32>) -> i32 {
+	// Create hashmap, let the key be the element in input array
+	// and value be its count. Then return the key with count of 1.
+    let mut occurances: HashMap<i32, i32> = HashMap::new();
+    for key in input {
+    *occurances.entry(key).or_insert(0) += 1;
+    }
+   let mut result: i32 = 0;
+    for (key, val) in occurances.iter() {
+        if *val == 1 {
+            result = key.to_owned();
+        }
+    }
+    return result
+}
+
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+	#[test] 
+	fn test_int() {
+		let expected = 5;
+		let input = vec![2, 3, 4, 2, 3, 5, 4, 6, 4, 6, 9, 10,9 ,8 ,7 ,8 ,10 ,7];
+		assert_eq!(expected.to_owned(), find_single(input));	
+	}
+}