重刷leetcode-day10-[111. 二叉树的最小深度]

【题目】111. 二叉树的最小深度

【题目考察】：二叉树

【目标复杂度】： O(n)

【解法一】：递归法

/**
 * 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 minDepth = function(root) {
    if (!root) {
        return 0;
    }
    
    const leftDepth = minDepth(root.left);
    const rightDepth = minDepth(root.right);

    if (!root.left && root.right) {
        return 1 + rightDepth;
    }

    if (!root.right && root.left) {
        return 1 + leftDepth;
    }

    return 1 + Math.min(leftDepth, rightDepth);
};

【解法二】：迭代法

/**
 * 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 minDepth = function(root) {
    if (!root) return 0;
    let depth = 0;
    const queue = [root];
    while(queue.length) {
        const size = queue.length;
        depth++;
        for(let i = 0; i < size; i++) {
            const front = queue.shift();
            if (front.left) queue.push(front.left);
            if (front.right) queue.push(front.right);

            if (!front.left && !front.right) {
                return depth;
            }
        }
    }

    return depth;
    
};