Added 70. Climbing Stairs Java (#71)

* Udating README.md (Added 70.Climbing Stairs)

* 70. Climbing Stairs(Java)

* Optimising 70. Climbing Stairs to O(1) space

* Changed space complexity of 70. Climbing Stairs

Author: PranayChauhan2516

Java/climbing-stairs.java

@@ -0,0 +1,12 @@
+class Solution {
+    public int climbStairs(int n) {
+        int prev1=1, prev2=2, cur=0;
+        if(n<=2) return n;
+        for(int i=3;i<=n;++i) {
+            cur=prev1+prev2;
+            prev1=prev2;
+            prev2=cur;
+        }
+        return cur;
+    }
+}

README.md

@@ -291,6 +291,7 @@ Check out ---> [Sample PR](https://github.com/codedecks-in/LeetCode-Solutions/pu
 | 72   | [Edit Distance](https://leetcode.com/problems/edit-distance/)                                 | [Python](./Python/edit-distance.py)            | _O(N\*M)_ | _O(n^2)_ | Medium     | Levenshtein Distance |      |
 | 91   | [Decode ways](https://leetcode.com/problems/decode-ways/)                                     | [Python](./Python/decode-ways.py)              | _O(N)_    | _O(N)_   | Easy       | DP                   |      |
 | 1025 | [Divisor Game](https://leetcode.com/problems/divisor-game/)                                   | [Python](./Python/divisor-game.py)             | _O(N^2)_  | _O(N)_   | Easy       | DP                   |      |
+| 070 | [Climbing Stairs](https://leetcode.com/problems/climbing-stairs/)                                   | [Java](./Java/climbing-stairs.java)             | _O(N)_  | _O(1)_  | Easy       | DP                   |      |
 
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