Solution1：二分查找 Recursive写法
思路：
Time Complexity: O(logN) Space Complexity: O(N) 递归缓存
Solution2：二分查找 Iterative写法
思路：
Time Complexity: O(logN) Space Complexity: O(1)
Solution1 Code：
class Solution1 {
public int closestValue(TreeNode root, double target) {
TreeNode next = target < root.val ? root.left : root.right;
if(next == null) return root.val;
int val_found = closestValue(next, target);
return Math.abs(val_found - target) < Math.abs(root.val - target) ? val_found : root.val;
}
}
Solution2 Code：
class Solution2 {
public int closestValue(TreeNode root, double target) {
if(root == null) return 0;
int closest = root.val;
TreeNode cur = root;
while(cur != null) {
if(Math.abs(cur.val - target) < Math.abs(closest - target)) closest = cur.val;
cur = target < cur.val ? cur.left : cur.right;
}
return closest;
}
}
