Since we are not allowed to rob two adjacent houses, we keep two variables pre and cur. During the i-th loop, pre records the maximum profit that we do not rob the i - 1-th house and thus the current house (the i-th house) can be robbed while cur records the profit that we have robbed the i - 1-th house.

The code is as follows.

1 class Solution { 2 public:  3     int rob(vector
     
      & nums) { 4         int n = nums.size(), pre = 0, cur = 0; 5         for (int i = 0; i < n; i++) { 6             int temp = max(pre + nums[i], cur); 7             pre = cur; 8             cur = temp; 9         }10         return cur;11     }12 };