*lintcode578- Lowest Common Ancestor III- medium

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */


public class Solution {
    /*
     * @param root: The root of the binary tree.
     * @param A: A TreeNode
     * @param B: A TreeNode
     * @return: Return the LCA of the two nodes.
     */
     
    private class ResultType{
        public boolean hasA, hasB;
        public TreeNode node;
        public ResultType(boolean hasA, boolean hasB, TreeNode node) {
            this.hasA = hasA;
            this.hasB = hasB;
            this.node = node;
        }
    }
    
    public TreeNode lowestCommonAncestor3(TreeNode root, TreeNode A, TreeNode B) {
        // write your code here
        ResultType result = findNode(root, A, B);
        if (result.hasA && result.hasB) {
            return result.node;
        }
        return null;
    }
    
    //ding yi定义
    //1. if has A, set hasA
    //2. if has B, set hasB
    //3. if (left.hasA&&right.hasB) || (left.hasB&&right.hasA) lca = root;
    private ResultType findNode(TreeNode root, TreeNode A, TreeNode B) {
        
        if (root == null) {
            return new ResultType(false, false, null);
        }
        
        ResultType left = findNode(root.left, A, B);
        ResultType right = findNode(root.right, A, B);
        
        boolean crtHasA = left.hasA || right.hasA || root == A;
        boolean crtHasB = left.hasB || right.hasB || root == B;
        
        if (root == A || root == B) {
            return new ResultType(crtHasA, crtHasB, root);
        }
        
        
        if (left.node != null && right.node != null) {
            return new ResultType(crtHasA, crtHasB, root);
        }
        
        if (left.node != null) {
            return new ResultType(crtHasA, crtHasB, left.node);
        }
        
        if (right.node != null) {
            return new ResultType(crtHasA, crtHasB, right.node);
        }
        
        return new ResultType(crtHasA, crtHasB, null);
    }
}