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binary_tree_level_order_traversalII.cpp
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60 lines (52 loc) · 1.33 KB
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/*
Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to right, level by level from leaf to root).
For example:
Given binary tree {3,9,20,#,#,15,7},
3
/ \
9 20
/ \
15 7
return its bottom-up level order traversal as:
[
[15,7]
[9,20],
[3],
]
*/
/**
* 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> > levelOrderBottom(TreeNode *root) {
queue<pair<TreeNode *, int> > q;
int level = 0;
vector<vector<int> > res;
vector<int> t;
if (root)
q.push(make_pair(root, 0));
while (!q.empty()) {
TreeNode *current = q.front().first;
int d = q.front().second;
q.pop();
if (d > level) {
level ++;
res.push_back(t);
t.clear();
}
t.push_back(current -> val);
if (current -> left) q.push(make_pair(current -> left, d + 1));
if (current -> right) q.push(make_pair(current -> right, d + 1));
}
if (t.size() > 0) res.push_back(t);
reverse(res.begin(), res.end());
return res;
}
};