Add 213 House Robber 2

Medium/HouseRobber2.java

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+/**
+ * Note: This is an extension of House Robber.
+ *
+ * After robbing those houses on that street, the thief has found himself a new place for his thievery so that he will
+ * not get too much attention. This time, all houses at this place are arranged in a circle. That means the first house
+ * is the neighbor of the last one. Meanwhile, the security system for these houses remain the same as for those in the
+ * previous street.
+ *
+ * Given a list of non-negative integers representing the amount of money of each house, determine the maximum amount of
+ * money you can rob tonight without alerting the police.
+ *
+ * Tags: Dynamic Programming
+ * Similar Problems: (E) House Robber, (M) Paint House, (E) Paint Fence, (M) House Robber III
+ */
+public class HouseRobber2 {
+
+    /**
+     * rob a circle can be divided into rob 2 rows
+     * 1. from 1st house to second last house
+     * 2. from 2nd house to last house
+     */
+    public int rob(int[] nums) {
+        if (nums == null || nums.length == 0) return 0;
+        if (nums.length == 1) return nums[0];
+        return Math.max(robRow(nums, 0, nums.length - 2), robRow(nums, 1, nums.length - 1));
+    }
+
+    private int robRow(int[] nums, int start, int end) {
+        int include = 0, exclude = 0;
+        for (int j = start; j <= end; j++) {
+            int i = include, e = exclude;
+            include = e + nums[j]; // include current number
+            exclude = Math.max(e, i); // the bigger of previous include and previous exclude
+        }
+        return Math.max(include, exclude);
+    }
+
+    public static void main(String[] args) {
+        HouseRobber2 hr = new HouseRobber2();
+        int res = hr.rob(new int[]{1, 2, 3, 4, 5});
+        System.out.println("rob: " + res);
+    }
+}