Algorithm ---> [queue structure] binary tree hierarchy traversal

Thinking

Use queue:

1. Initialization of the root, push into the queue q
2. Circular queues q, when one is not empty, to take the first element (q.shift), referred to as r
3. If r.left is not empty, the r.left advance q, if r.right is not empty, the r.right advance q

Record level:
4. 0 = initial setting I;
5. The enqueued when enqueuing an object {r: root, i}
6. dequeued using es6 deconstruction assignment taken {r, i}

• To achieve the following:

var averageOfLevels = function (root) {
	let q = []; 		// 队列
	let i = 0;		// 记录层次用的标记
	q.push({r: root, i});		// 将根放入队列中
	while(q.length > 0) {		// 队列不为空
		let { r, i } = q.shift();		// 得到根和层次信息
		if(r) {		// 根不为空
			i++;		// 层次加1
			if(r.left) {		// 左孩子不为空
				q.push(r.left);
			}
			if(r.right) {
				.push(r.right);		
			}
			console.log(r.val, i);
		}
	}
}

• The above has been achieved basically traverse the level
• The following returns a new array, the subject needs to achieve

1. Now it has the value of each layer and the layer number.
2. The next layer of each layer and the number of key values ​​into a map structure.

var averageOfLevels = function (root) {
    let q = [];
    let i = 0;
    let map = new Map;
    q.push({ r: root, i });
    while (q.length > 0) {
        let { r, i } = q.shift();
        if (r) {
            i++;
            if (r.left) {
                q.push({ r: r.left, i });
            }
            if (r.right) {
                q.push({ r: r.right, i });
            }
            // 改动部分, 使用map结构存储层次的 键值对
            if(map.has(i)){
                let arr = map.get(i);
                arr.push(r.val);
                map.set(i, arr);
            } else{
                map.set(i,[r.val]);
            }
        }
    }
    for(let [i, key] of map){
        console.log(i, key);
    }
};

• Above the completion of each layer and the number of key values ​​into a map structure.
• Modify the end of the following for(let [i, key] of map)internal, to meet the needs of the subject

let retArr = [];
for (let [i, key] of map) {
    let sum = 0;
    if (key.length > 1) {
        for (let i = 0; i < key.length; i++) {
            sum += key[i];
        }
    } else {
        sum = key[0];
    }
    retArr[i - 1] = sum / key.length;
}
return retArr