Added LC 70 java solution (#143)

Author: Tahanima

Algorithms/Easy/70_ClimbingStairs/Solution.java

@@ -0,0 +1,29 @@
+class Solution {
+    int n;
+    int[] memo = new int[50];
+
+    private int solve(int step) {
+        if (step == n) {
+            return 1;
+        } else if (step > n) {
+            return 0;
+        } else if (memo[step] != -1) {
+            return memo[step];
+        } else {
+            memo[step] = solve(step + 1) + solve(step + 2);
+            
+            return memo[step];
+        }
+    }
+
+
+    public int climbStairs(int n) {
+        this.n = n;
+
+        for (int i = 0; i < 50; i++) {
+            memo[i] = -1;
+        }
+
+        return solve(0);
+    }
+}