算法题-找出二叉树的第几个最小值

// 例如：    5
//       3     7
//     2  4   6  8
// 第二小值 3
// 树的中序遍历是由小到大
export const arr:number[] = []
export const tree:INode = {
    value:5,
    left:{
        value:3,
        left:{
            value:2,
        },
        right:{
            value:4,
        }
    },
    right:{
        value:7,
        left:{
            value:6,
        },
        right:{
            value:8,
        }
    }
}

export interface INode {
    value:number;
    left?:INode;
    right?:INode;
}
export function preOrder(tree:INode|undefined) {
    if(!tree) return
    // console.log(tree.value)
    preOrder(tree?.left)
    preOrder(tree?.right)
}
export function inOrder(tree:INode|undefined) {
    if(!tree) return
    inOrder(tree?.left)
    // console.log(tree.value)
    arr.push(tree.value)
    inOrder(tree?.right)
}
export function postOrder(tree:INode|undefined) {
    if(!tree) return
    postOrder(tree?.left)
    postOrder(tree?.right)
    // console.log(tree.value)
}