層序遍歷二叉樹VS之字形遍歷二叉樹

1. 層序遍歷二叉樹

 C++ 代碼

vector<vector<int> > levelTraversal(TreeNode* pRoot) { // 層序遍歷二叉樹
    vector<vector<int> > result;
    if(pRoot != NULL) {
        queue<TreeNode*> q;
        q.push(pRoot);
        int levelWith = 0;
        int n = 1;
        vector<int> v;
        while(!q.empty()) {
            TreeNode* p = q.front();
            v.push_back(p->val);
            if(p->left) {
                q.push(p->left);
                ++levelWith;
            }
            if(p->right) {
                q.push(p->right);
                ++levelWith;
            }
            q.pop();
            --n;
            if(0 == n) {
                result.push_back(v);
                v.resize(0);
                n = levelWith;
                levelWith = 0;
            }
        }
    }
    return result;
}

2. 之字形遍歷二叉樹

C++ 代碼

vector<vector<int> > zigzag(TreeNode* pRoot) {// 按之字形順序遍歷二叉樹
    vector<vector<int> > result;
    if(NULL == pRoot) return result;
    stack<TreeNode*> s1/*從右到左壓入*/, s2/*從左到右壓入*/;
    s1.push(pRoot);
    vector<int> vec;
    while(!s1.empty() || !s2.empty()) {
        while(!s1.empty()) {
            TreeNode* node = s1.top();
            vec.push_back(node->val);
            if(node->left)
                s2.push(node->left);
            if(node->right)
                s2.push(node->right);
            s1.pop();
        }
        result.push_back(vec);
        vec.resize(0);
        while(!s2.empty()) {
            TreeNode* node = s2.top();
            vec.push_back(node->val);
            if(node->right)
                s1.push(node->right);
            if(node->left)
                s1.push(node->left);
            s2.pop();
        }
        result.push_back(vec);
        vec.resize(0);
    }
    return result;
}