题解 | #判断是不是二叉搜索树# | Rust

/**
 * #[derive(PartialEq, Eq, Debug, Clone)]
 * pub struct TreeNode {
 *     pub val: i32,
 *     pub left: Option<Box<TreeNode>>,
 *     pub right: Option<Box<TreeNode>>,
 * }
 *
 * impl TreeNode {
 *     #[inline]
 *     fn new(val: i32) -> Self {
 *         TreeNode {
 *             val: val,
 *             left: None,
 *             right: None,
 *         }
 *     }
 * }
 */
struct Solution{

}

impl Solution {
    fn new() -> Self {
        Solution{}
    }

    /**
    * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
    *
    * 
        * @param root TreeNode类 
        * @return bool布尔型
    */
    pub fn isValidBST(&self, root: Option<Box<TreeNode>>) -> bool {
        let mut pre = i32::MAX;
        let mut ans = true;
        Solution::dfs(root, &mut pre, &mut ans);
        return ans;
    }
    fn dfs(mut node: Option<Box<TreeNode>>, pre: &mut i32, ans: &mut bool) {
        if node.is_none() {
            return;
        }
        Solution::dfs(node.as_mut().unwrap().left.take(), pre, ans);
        if *pre != i32::MAX {
            if *pre > node.as_ref().unwrap().val {
                *ans = false;
            }
        }
        *pre = node.as_ref().unwrap().val;
        Solution::dfs(node.as_mut().unwrap().right.take(), pre, ans);
    }
}