leetcode Binary Tree Breadth-First Search

leetcode 199题

Posted by franki on September 5, 2021

leetcode 199题 二叉树的右视图

给定一个二叉树的 根节点 root，想象自己站在它的右侧，按照从顶部到底部的顺序，返回从右侧所能看到的节点值。

示例 1：

输入: [1,2,3,null,5,null,4]
输出: [1,3,4]

示例 2：

输入: [1,null,3]
输出: [1,3]

示例 3：

输入: []
输出: []

思路

bfs

代码

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number[]}
 */
function rightSideView(root) {
    if (root === null) {
        return [];
    }

    const queue = [root];
    let temp = [];
    const res = [];
    let curNum = 1;
    let nextNum = 0;

    while (queue.length !== 0) {
        if (curNum > 0) {
            const node = queue.shift();
            if (node.left) {
                queue.push(node.left);
                nextNum++;
            }
            if (node.right) {
                queue.push(node.right);
                nextNum++;
            }
            curNum--;
            temp.push(node.val);
        }
        if (curNum === 0) {
            res.push(temp[temp.length-1]);
            curNum = nextNum;
            nextNum = 0;
            temp = [];
        }
    }
    return res;
}

复杂度分析

  • 时间复杂度：O(N)
  • 空间复杂度：O(N)
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