树形动态规划

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public int rob(TreeNode root) {
        f = new HashMap<TreeNode, int[]>();
        f.put(null, new int[]{0, 0});
        dfs(root);
        return Math.max(f.get(root)[0], f.get(root)[1]);
    }
    private void dfs(TreeNode root) {
        if(root == null) return;
        f.put(root, new int[2]);
        dfs(root.left);
        dfs(root.right);
        f.get(root)[0] = 
            Math.max(f.get(root.left)[0], f.get(root.left)[1]) +
            Math.max(f.get(root.right)[0], f.get(root.right)[1]);
        f.get(root)[1] = 
            f.get(root.left)[0] + f.get(root.right)[0] + root.val;
    }
    HashMap<TreeNode, int[]> f; 
}

class Solution {
public:
    unordered_map <TreeNode*, int> f, g;
    void dfs(TreeNode* node) {
        if (!node) {
            return;
        }
        dfs(node->left);
        dfs(node->right);
        f[node] = node->val + g[node->left] + g[node->right];
        g[node] = max(f[node->left], g[node->left]) + max(f[node->right], g[node->right]);
    }
    int rob(TreeNode* root) {
        dfs(root);
        return max(f[root], g[root]);
    }
};