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??????????????????????????????ο????á?Cracking the Coding Interview???????????

??????????????????????????????????????????t???????????p??q???м?????p

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????????????????????????????????????????????????????????????????p??q??·???????????????

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???????????????????????????????????????????p??q??????????????????????p??q??????????????????????в??????????

????????????????????????в?????????????p??q????????????????????????????????

???????????????????????￡?

????[cpp] view plaincopyprint?

????/* ??p?root??????????true */

????boolean covers(TreeNode root?? TreeNode p) {

????if (root == null) return false;

????if (root == p) return true;

????return covers(root.left?? p) || covers(root.right?? p);

????}

????TreeNode commonAncestorHelper(TreeNode root?? TreeNode p??

????TreeNode q) {

????if (root == null) return null;

????if (root == p || root == q) return root;

????boolean is_p_on_left = covers(root.left?? p);

????boolean is_q_on_left = covers(root.left?? q);

????/* ??p??q?????????????root */

????if (is_p_on_left != is_q_on_left) return root;

????/* ????????????????????? */

????TreeNode child_side = is_p_on_left ? root.left : root.right;

????return commonAncestorHelper(child_side?? p?? q);

????}

????TreeNode commonAncestor(TreeNode root?? TreeNode p?? TreeNode q) {

????if (!covers(root?? p) || !covers(root?? q)) { // ??????

????return null;

????}

????return commonAncestorHelper(root?? p?? q);

????}