扁平陣列和樹形結構的相互轉換

扁平陣列轉換為樹形結構(1)

這個是最常用的，當我們從後臺獲取一個扁平陣列的時候，通常比如用id、pid來標識父子關係，如：

var arr = [{id: 1, pid: '-1'},{id: 11, pid: '1'},{id: 12, pid: '1'}]

用map記錄的方法是最常用效果也最好的複雜度是O(nlgn),支援多個根節點:

function listToTree(list) {
    var map = {}, node, tree= [], i;
    for (i = 0; i < list.length; i ++) {
        map[list[i].id] = list[i]; 
        list[i].children = []; 
    }
    for (i = 0; i < list.length; i += 1) {
        node = list[i];
        if (node.pid !== '-1') {
            map[node.pid].children.push(node);
        } else {
            tree.push(node);
        }
    }
    return tree;
}

listToTree(arr); //[{"id":1,"pid":"-1","children":[{"id":11,"pid":"1","children":[]},{"id":12,"pid":"1","children":[]}]}]
 

但是專案中有個需求，在後臺沒有返回給帶層級資訊level的時候，需要用到層級資訊，這樣轉換沒法計算出層級，因此就需要用迭代的方法了，預設根節點層級為0，依次遞增：

function listToTreeWithLevel(list, parent, level) {
    var out = []
    for (var node of list) {  
            if (node.pid == parent) {
                node.level = level;
                var children = listToTreeWithLevel(list, node.id, level + 1)
                if (children.length) {
                    node.children = children
                }
                out.push(node)
            }
    }
    return out
}

listToTreeWithLevel(arr, '-1', 0) //[{"id":1,"pid":"-1","children":[{"id":11,"pid":"1","children":[],"level":1},{"id":12,"pid":"1","children":[],"level":1}],"level":0}]
 

扁平陣列轉換為樹形結構(2)

fnSetTreeData(list) {
var data = [...list];
data.forEach(father => {
var branchArr = data.filter(child => {
if (father.id == child.parentId) {
child.hasParent = true;
}
return father.id == child.parentId;
});

if (branchArr.length > 0) father.children = branchArr;
});
return data.filter(item => {
return !item.hasParent;
});
}

樹形結構轉換為扁平陣列

這個其實就是資料結構中的廣度優先遍歷：

function treeToList(tree) {
  var queen = [];
  var out = [];
  queen = queen.concat(tree);
  while(queen.length) {
      var first = queen.shift();
    if (first.children) {
        queen = queen.concat(first.children)
      delete first['children'];
    }
    
    out.push(first);
  }
  return out;
}

var tree = [{"id":1,"pid":"-1","children":[{"id":11,"pid":"1","children":[]},{"id":12,"pid":"1","children":[]}]}];
treeToList(tree) //[{"id":1,"pid":"-1"},{"id":11,"pid":"1"},{"id":12,"pid":"1"}]