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111.minimum-depth-of-binary-tree.cpp
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91 lines (82 loc) · 2.04 KB
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// Tag: Tree, Depth-First Search, Breadth-First Search, Binary Tree
// Time: O(N)
// Space: O(W)
// Ref: -
// Note: -
// Given a binary tree, find its minimum depth.
// The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.
// Note: A leaf is a node with no children.
//
// Example 1:
//
//
// Input: root = [3,9,20,null,null,15,7]
// Output: 2
//
// Example 2:
//
// Input: root = [2,null,3,null,4,null,5,null,6]
// Output: 5
//
//
// Constraints:
//
// The number of nodes in the tree is in the range [0, 105].
// -1000 <= Node.val <= 1000
//
//
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode() : val(0), left(nullptr), right(nullptr) {}
* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
* };
*/
class Solution {
public:
int minDepth(TreeNode* root) {
if (!root) {
return 0;
}
if (!root->left) {
return minDepth(root->right) + 1;
}
if (!root->right) {
return minDepth(root->left) + 1;
}
return min(minDepth(root->left), minDepth(root->right)) + 1;
}
};
class Solution {
public:
int minDepth(TreeNode* root) {
if (!root) {
return 0;
}
queue<TreeNode *> q;
q.push(root);
int level = 0;
while (!q.empty()) {
int count = q.size();
level++;
for (int i = 0; i < count; i++) {
TreeNode *cur = q.front();
q.pop();
if (!cur->left && !cur->right) {
return level;
}
if (cur->left) {
q.push(cur->left);
}
if (cur->right) {
q.push(cur->right);
}
}
}
return -1;
}
};