Chapter 09 section 02 C++ codes updated. Java codes added.

Author: liuyubobobo

09-Dynamic-Programming/Course Code (Java)/02-Climbing-Stairs/src/Solution1.java

@@ -0,0 +1,31 @@
+import java.util.Arrays;
+
+/**
+ * Created by liuyubobobo.
+ */
+public class Solution1 {
+
+    private int[] memo;
+
+    public int climbStairs(int n) {
+        memo = new int[n+1];
+        Arrays.fill(memo, -1);
+        return calcWays(n);
+    }
+
+    private int calcWays(int n){
+
+        if(n == 0 || n == 1)
+            return 1;
+
+        if(memo[n] == -1)
+            memo[n] = calcWays(n - 1) + calcWays(n - 2);
+
+        return memo[n];
+    }
+
+    public static void main(String[] args) {
+
+        System.out.println((new Solution1()).climbStairs(10));
+    }
+}

09-Dynamic-Programming/Course Code (Java)/02-Climbing-Stairs/src/Solution2.java

@@ -0,0 +1,22 @@
+/// 70. Climbing Stairs
+/// https://leetcode.com/problems/climbing-stairs/description/
+/// 动态规划
+/// 时间复杂度: O(n)
+/// 空间复杂度: O(n)
+public class Solution2 {
+
+    public int climbStairs(int n) {
+
+        int[] memo = new int[n + 1];
+        memo[0] = 1;
+        memo[1] = 1;
+        for(int i = 2 ; i <= n ; i ++)
+            memo[i] = memo[i - 1] + memo[i - 2];
+        return memo[n];
+    }
+
+    public static void main(String[] args) {
+
+        System.out.println((new Solution2()).climbStairs(10));
+    }
+}