利用层次遍历原理构建二叉树

层次遍历构建二叉树:

1.定义二叉树节点:

function TreeNode(val){
    this.val = val;
    this.left = this.right = null;
}

2.层次遍历构建二叉树：

function createTree(arr){
    if(!arr||!arr.length)return null;
    var root = new TreeNode(arr.shift());
    var list = [root];
    while(arr.length){
        var tmpList = [];
        for(var i=0;i<list.length;i++){
            var p = list[i];
            var left = arr.shift();
            if(left!==null){
                p.left = new TreeNode(left);
            }
            var right = arr.shift();
            if(right!==null){
                p.right = new TreeNode(right);
            }
            if(p.left){
               tmpList.push(p.left);
            }
            if(p.right){
               tmpList.push(p.right);
            }
        }
        list = tmpList;
    }
    return root;
}

3.测试

//var arr = [1,2,2,3,4,4,3];
var arr = [1,2,2,null,3,null,3];
var root = createTree(arr);
console.log(root);