add merge sort tpl code

Author: cch123

SORT/ms.rs

@@ -0,0 +1,39 @@
+fn main() {
+    let mut a = vec![4,4,3,2,1];
+    ms(&mut a);
+    println!("{:?}",a);
+}
+
+fn ms(arr: &mut Vec<i32>) {
+    if arr.len() == 0 || arr.len() == 1 {
+        return
+    }
+
+    let mid = arr.len()/2;
+    let (l,r ) = arr.split_at_mut(mid);
+    let (mut l, mut r) = (l.to_vec(), r.to_vec());
+
+    ms(&mut l);
+    ms(&mut r);
+
+    let (mut x,mut y, mut merged) = (0,0, vec![]);
+    while x < l.len() && y < r.len() {
+        if *l.get(x).unwrap() < *r.get(y).unwrap() {
+            merged.push(*l.get(x).unwrap());
+            x += 1;
+        } else {
+            merged.push(*r.get(y).unwrap());
+            y+=1;
+        }
+    }
+    while x < l.len() {
+        merged.push(*l.get(x).unwrap());
+        x += 1;
+    }
+    while y < r.len() {
+        merged.push(*r.get(y).unwrap());
+        y+=1;
+    }
+
+    std::mem::replace(arr, merged);
+}