[LeetCode] 173. Binary Search Tree Iterator, Medium

1. 문제

• 이진 탐색 트리가 주어질 때, 중위 순회를 수행하여 요구사항을 만족하는 class를 구현하라.

2. 해결

/**
 * Definition for a binary tree node.
 * class TreeNode {
 *     val: number
 *     left: TreeNode | null
 *     right: TreeNode | null
 *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
 *         this.val = (val===undefined ? 0 : val)
 *         this.left = (left===undefined ? null : left)
 *         this.right = (right===undefined ? null : right)
 *     }
 * }
 */

class BSTIterator {
    pointer: number;
    travalArr: number[]
    constructor(root: TreeNode | null) {
        const traval = [];

        function DFS(node: TreeNode | null) {
            if(!node) return;
            
            DFS(node.left);
            traval.push(node.val);
            DFS(node.right);    
        }

        DFS(root);
        this.travalArr = traval;
        this.pointer = -1;
    }

    next(): number {
        return this.travalArr[++this.pointer];
    }

    hasNext(): boolean {
        return this.pointer + 1 < this.travalArr.length;
    }
}

/**
 * Your BSTIterator object will be instantiated and called as such:
 * var obj = new BSTIterator(root)
 * var param_1 = obj.next()
 * var param_2 = obj.hasNext()
 */

• 초기화 시점에 중위 순회를 통해 value를 배열에 담아두고, pointer는 -1로 초기화.