Add climbing stairs (#4168)

src/main/java/com/thealgorithms/dynamicprogramming/ClimbingStairs.java

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+package com.thealgorithms.dynamicprogramming;
+
+/* A DynamicProgramming solution for Climbing Stairs' problem Returns the
+    distinct ways can you climb to the staircase by either climbing 1 or 2 steps.
+
+    Link : https://medium.com/analytics-vidhya/leetcode-q70-climbing-stairs-easy-444a4aae54e8
+*/
+public class ClimbingStairs {
+
+    public static int numberOfWays(int n) {
+
+        if(n == 1 || n == 0){
+            return n;
+        }
+        int prev = 1;
+        int curr = 1;
+
+        int next;
+
+        for(int i = 2; i <= n; i++){
+            next = curr+prev;
+            prev = curr;
+
+            curr = next;
+        }
+
+        return curr;
+
+    }
+}

src/test/java/com/thealgorithms/dynamicprogramming/climbStairsTest.java

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+package com.thealgorithms.dynamicprogramming;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+
+public class climbStairsTest {
+
+    @Test
+    void climbStairsTestForTwo(){assertEquals(2, ClimbingStairs.numberOfWays(2));}
+
+    @Test
+    void climbStairsTestForZero(){assertEquals(0, ClimbingStairs.numberOfWays(0));}
+
+    @Test
+    void climbStairsTestForOne(){assertEquals(1, ClimbingStairs.numberOfWays(1));}
+
+    @Test
+    void climbStairsTestForFive(){assertEquals(8, ClimbingStairs.numberOfWays(5));}
+
+    @Test
+    void climbStairsTestForThree(){assertEquals(3, ClimbingStairs.numberOfWays(3));}
+}