create 0070-climbing-stairs.dart

Author: bansalgaurav852

Diff for: dart/0070-climbing-stairs.dart

@@ -0,0 +1,13 @@
+class Solution {
+  int climbStairs(int n) {
+      int first=0;
+      int second=1;
+      int res=1;
+      for(int i=0;i<n;i++){
+        res=first+second;
+        first=second;
+        second=res;
+      }
+    return res;
+  }
+}