House Robber

dp with rolling array
The index of dp array is calculated by the original index mod 2.

public class Solution {
    /**
     * @param A: An array of non-negative integers.
     * return: The maximum amount of money you can rob tonight
     */
    public long houseRobber(int[] A) {
        // write your code here
        if (A == null || A.length == 0) return 0;
        long[] dp = new long[2];
        dp[0] = 0;
        dp[1] = A[0];
        for (int i = 2; i <= A.length; i++) {
            dp[i % 2] = Math.max(dp[(i - 1) % 2], dp[i % 2] + A[i - 1]);
        }
        return dp[A.length % 2];
    }
}