0198-house-robber.java

class Solution {

    public int rob(int[] nums) {
        if (nums == null || nums.length == 0) return 0;
        if (nums.length == 1) return nums[0];
        if (nums.length == 2) return Math.max(nums[0], nums[1]);

        int robWithOutIncludingLastHouse = 0, robWithIncludingLastHouse = 0;

        for (int n : nums) {
            int temp = Math.max(
                robWithOutIncludingLastHouse + n,
                robWithIncludingLastHouse
            );
            robWithOutIncludingLastHouse = robWithIncludingLastHouse;
            robWithIncludingLastHouse = temp;
        }
        return robWithIncludingLastHouse;
    }

    public int robDP(int[] nums) {
        if (nums == null || nums.length == 0) return 0;
        if (nums.length == 1) return nums[0];
        if (nums.length == 2) return Math.max(nums[0], nums[1]);

        int[] dp = new int[nums.length];
        dp[0] = nums[0];
        dp[1] = Math.max(nums[0], nums[1]);

        for (int i = 2; i < nums.length; i++) {
            dp[i] = Math.max(dp[i - 1], dp[i - 2] + nums[i]);
        }
        return dp[nums.length - 1];
    }

    // DP with O(1) space
    public int robDP2(int[] nums) {
        if (nums == null || nums.length == 0) return 0;

        int dp0 = 0, dp1 = 0, curr;

        for (int i = 0; i < nums.length; i++) {
            curr = Math.max(dp0 + nums[i], dp1);
            dp0 = dp1;
            dp1 = curr;
        }
        return Math.max(dp0, dp1);
    }
}