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HouseRobber.java
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HouseRobber.java
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class HouseRobber {
// 1. dp
static class Res {
int rob;
int unRob;
Res(int rob, int unRob) {
this.rob = rob;
this.unRob = unRob;
}
}
public int rob1(TreeNode root) {
if (root == null) return 0;
Res res = robTree(root);
return Math.max(res.rob, res.unRob);
}
private Res robTree(TreeNode root) {
if (root == null) {
return new Res(0, 0);
}
Res left = robTree(root.left);
Res right = robTree(root.right);
int rob = left.unRob + right.unRob + root.val;
int unRob = Math.max(left.rob, left.unRob) + Math.max(right.rob, right.unRob);
return new Res(rob, unRob);
}
// 2. backtracking + memoization
Map<TreeNode, Integer> map = new HashMap<>();
public int rob2(TreeNode root) {
if (root == null) return 0;
// memo
if (map.get(root) != null) return map.get(root);
int rob = root.val;
if (root.left != null) {
rob += rob2(root.left.left) + rob2(root.left.right);
}
if (root.right != null) {
rob += rob2(root.right.left) + rob2(root.right.right);
}
int notRob = rob2(root.left) + rob2(root.right);
int val = Math.max(rob, notRob);
// memo
map.put(root, val);
return val;
}
}