leetcode 之 公共祖先以及路径类型相关

公共祖先和路径两种类型写在一起

235. 二叉搜索树的最近公共祖先

235. 二叉搜索树的最近公共祖先

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */

/**
 * @param {TreeNode} root
 * @param {TreeNode} p
 * @param {TreeNode} q
 * @return {TreeNode}
 */
var lowestCommonAncestor = function(root, p, q) {
    if (!root) return null;
    const dfs = (node) => {
        if (node == null) return null;
        if (node.val == p.val || node.val == q.val) {
            return node;
        }
        const left = dfs(node.left);
        const right = dfs(node.right);
        if (left && right) {
            return node;
        }
        if (left == null) {
            return right;
        }
        return left;
    }
    return dfs(root);
};

236. 二叉树的最近公共祖先

236. 二叉树的最近公共祖先

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @param {TreeNode} p
 * @param {TreeNode} q
 * @return {TreeNode}
 */
var lowestCommonAncestor = function(root, p, q) {
    if(root == null) return null;
    const dfs = (node) => {
        if (node == null) return null;
        if (node == p || node == q) {
            return node;
        }
        let left = dfs(node.left);
        let right = dfs(node.right);
        if (left && right) {
            return node;
        }
        if(left == null) {
            return right;
        }
        return left;
    };
    return dfs(root);
};

129. 求根节点到叶节点数字之和

129. 求根节点到叶节点数字之和

/**
 * 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}
 */
var sumNumbers = function(root) {
    if (root == null) return 0;
    let path = [];
    const DFS = (node, sum) => {
        if (node == null) return;
        if (node.left == null && node.right == null) {
            sum = sum * 10 + node.val;
            path.push(sum);
        }

        sum = sum * 10 + node.val;
        node.left && DFS(node.left, sum);
        node.right && DFS(node.right, sum);
    }
    DFS(root, 0);
    return path.reduce((prev, next) => {
        return prev+next;
    }, 0);
};

257. 二叉树的所有路径

257. 二叉树的所有路径

/**
 * 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 {string[]}
 */
var binaryTreePaths = function(root) {
    if (root == null) return [];
    let res = [];
    const DFS = (node, arr) => {
        if (!node) return;
        arr.push(node.val);
        if (node.left == null && node.right == null) {
            let str = arr.join('->');
            res.push(str);
        }
        node.left && DFS(node.left, arr);
        node.right && DFS(node.right, arr);
        arr.pop();
    }
    DFS(root, []);
    return res;
};