diff --git a/Week_04/id_115/leetcode_309_115.java b/Week_04/id_115/leetcode_309_115.java
new file mode 100644
index 00000000..cfeacc09
--- /dev/null
+++ b/Week_04/id_115/leetcode_309_115.java
@@ -0,0 +1,23 @@
+class Solution {
+	public int maxProfit(int[] prices) {
+        if (prices.length<2) return 0;
+        
+        int buy[]=new int[prices.length];
+        int sell[]=new int[prices.length];
+        //day0
+        buy[0] = -prices[0];
+        sell[0]= 0;
+    
+        //day1
+        buy[1] =  Math.max(buy[0],-prices[1]);
+        sell[1]=  Math.max(sell[0],buy[0]+prices[1]); 
+      
+        for(int i =2;i<prices.length;i++){    
+          buy[i]  =Math. max( buy[i - 1], sell[i - 2] - prices[i]);   
+            sell[i] =Math. max(sell[i - 1],  buy[i - 1] + prices[i]);   
+          
+        }
+        return sell[prices.length-1];
+        
+    }
+}
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diff --git a/Week_04/id_115/leetcode_746_115.java b/Week_04/id_115/leetcode_746_115.java
new file mode 100644
index 00000000..b8ab7a43
--- /dev/null
+++ b/Week_04/id_115/leetcode_746_115.java
@@ -0,0 +1,11 @@
+class Solution {
+    public int minCostClimbingStairs(int[] cost) {
+  int[] f = new int[cost.length + 1];//到达每层楼最小花费
+        f[0] = 0;
+        f[1] = 0;
+        for (int i = 2; i <= cost.length; i++) {
+            f[i] = Math.min(f[i - 1] + cost[i - 1], f[i - 2] + cost[i - 2]);
+        }
+        return f[cost.length];
+    }
+}
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