binary-tree-level-order-traversal

最新推荐文章于 2019-10-25 10:23:32 发布

原创最新推荐文章于 2019-10-25 10:23:32 发布 · 268 阅读

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本文介绍了一种实现树的层次遍历的算法，并通过C++代码详细展示了该算法的具体实现过程。考虑到空树的情况，文章特别强调了使用Vector进行节点存储时的操作细节。

题目没什么说的就是树的层次遍历，但是要考虑树为空的情况。而且对于Vector必须是先申请一个小Vector，对其操作完成后再将其加入大的Vector中。不能V[i].push_back（）,因为这时候V[i]还不存在。

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
vector<vector<int> > levelOrder(TreeNode *root) {
        queue<TreeNode* > Q;
        vector<vector<int> >V;
        Q.push(root);
        if (root==NULL) return V;
        queue<TreeNode*> tmp ;
        while(!Q.empty()) {
            vector<int> v1;
            while(!Q.empty()) {
                TreeNode* pn = Q.front(); Q.pop();
                v1.push_back(pn->val);
                if (pn->left)
                tmp.push(pn->left);
                if (pn->right)
                tmp.push(pn->right);                
            }
            V.push_back(v1);
            while (!tmp.empty()) {
                Q.push(tmp.front());
                tmp.pop();
            }

        }
        return V;
}
};

测试代码

 #include <queue>
 #include <iostream>
 #include <vector>
using namespace std;

 struct TreeNode {
     int val;
     TreeNode *left;
     TreeNode *right;
     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};


vector<vector<int> > levelOrder(TreeNode *root) {
        queue<TreeNode* > Q;
        vector<vector<int> >V;
        Q.push(root);
        if (root==NULL) return V;
        queue<TreeNode*> tmp ;
        while(!Q.empty()) {
            vector<int> v1;
            while(!Q.empty()) {
                TreeNode* pn = Q.front(); Q.pop();
                v1.push_back(pn->val);
                if (pn->left)
                tmp.push(pn->left);
                if (pn->right)
                tmp.push(pn->right);                
            }
            V.push_back(v1);
            while (!tmp.empty()) {
                Q.push(tmp.front());
                tmp.pop();
            }

        }
        return V;
}

int main() {
    TreeNode* h = new TreeNode (1);
    h->right  = new TreeNode(2);
    h->left = new TreeNode(3);
    h->right->left = new TreeNode(4);
    h->right->left->left = new TreeNode(5);
    vector<vector<int>> V = levelOrder(h);
    for (int i=0;i<V.size();i++) {
        for (int j=0;j<V[i].size();j++) {
            cout<<V[i][j] <<" ";
        }
        cout<<endl;
    }
}