diff --git a/OJ notes/pages/Leetcode House-Robber.md b/OJ notes/pages/Leetcode House-Robber.md
index cac63e5..2bfde04 100644
--- a/OJ notes/pages/Leetcode House-Robber.md	
+++ b/OJ notes/pages/Leetcode House-Robber.md	
@@ -145,3 +145,39 @@ public:
 
 ```cpp
 
+```
+
+#### Stage 4:
+
+```cpp
+class Solution {
+public:
+  int rob(vector<int> &nums) {
+    // iterative, from the buttom up
+    // We can utilize the hash map feature
+
+    int size = nums.size();
+    if (size == 0) {
+      return 0;
+    } else if (size == 1) {
+      return nums[0];
+    }
+
+    int prev1, prev2, next; // next: i + 1
+
+    int curLoc = 1;
+    prev1 = nums[0];               // i - 1
+    prev2 = max(nums[0], nums[1]); // i
+    next = prev2;
+    while (curLoc < size - 1) {
+      // cache[curLoc + 1] = max(cache[curLoc - 1] + nums[curLoc + 1] ,
+      // cache[curLoc]);
+      next = max(prev1 + nums[curLoc + 1], prev2);
+      prev1 = prev2;
+      prev2 = next;
+      curLoc++;
+    }
+    return next;
+  }
+};
+```
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