add solution 021[js]

Author: limbowandering

solution/021.Merge Two Sorted Lists/Solution.js

@@ -0,0 +1,57 @@
+const mergeTwoLists2 = function (l1, l2) {
+  if (l1 === null && l2 === null) {
+    return null;
+  }
+  if (l1 !== null && l2 === null) {
+    return l1;
+  }
+  if (l1 === null && l2 !== null) {
+    return l2;
+  }
+  if (l1 !== null && l2 !== null) {
+    let t = null, h = null;
+    if (l1.val > l2.val) {
+      t = l2;
+      h = l2;
+      l2 = l2.next;
+    } else {
+      t = l1;
+      h = l1;
+      l1 = l1.next;
+    }
+    while (l1 !== null && l2 !== null) {
+      if (l1.val > l2.val) {
+        t.next = l2;
+        t = t.next;
+        l2 = l2.next;
+      } else {
+        t.next = l1;
+        t = t.next;
+        l1 = l1.next;
+      }
+    }
+    while (l1 !== null) {
+      t.next = l1;
+      l1 = l1.next;
+      t = t.next;
+    }
+    while (l2 !== null) {
+      t.next = l2;
+      l2 = l2.next;
+      t = t.next;
+    }
+    return h;
+  }
+}
+
+const mergeTwoLists = function (l1, l2) {
+  if (l1 === null) return l2;
+  if (l2 === null) return l1;
+  if (l1.val < l2.val) {
+    l1.next = mergeTwoLists(l1.next, l2);
+    return l1;
+  } else {
+    l2.next = mergeTwoLists(l1, l2.next);
+    return l2;
+  }
+}