packageeasy;

importjava.util.LinkedList;

importjava.util.Queue;

importclasses.TreeNode;

publicclassMinimumDepthofBinaryTree {

publicintminDepth(TreeNoderoot) {

if(root ==null)return0;

intleft =minDepth(root.left);

intright =minDepth(root.right);

if(left ==0)returnright+1;

if(right ==0)returnleft+1;

returnMath.min(left,right)+1;

}

publicstaticvoidmain(String[]args){

MinimumDepthofBinaryTreetest =newMinimumDepthofBinaryTree();

TreeNoderoot =newTreeNode(1);

root.left =newTreeNode(2);

root.right =newTreeNode(3);

System.out.println(test.minDepth(root));

}

publicintminDepth_BFS(TreeNoderoot) {

if(root ==null)return0;

Queue<TreeNode>q =newLinkedList();

q.offer(root);

intlevel =0;

while(!q.isEmpty()){

level++;

intsize =q.size();

for(inti =0;i <size;i++){

TreeNodecurr =q.poll();

if(curr.left !=null)q.offer(curr.left);

if(curr.right !=null)q.offer(curr.right);

if(curr.left ==null &&curr.right ==null)returnlevel;

}

}

returnlevel;

}

}

|121|[Best Time to Buy and Sell Stock](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/)|[Solution](../../blob/master/EASY/src/easy/BestTimeToBuyAndSellStock.java)| O(n)|O(1) | Easy| DP

|117|[Populating Next Right Pointers in Each Node II](https://leetcode.com/problems/populating-next-right-pointers-in-each-node-ii/)|[Solution](../../blob/master/HARD/src/hard/PopulatingNextRightPointersinEachNodeII.java)| O(n)|O(1) | Hard| BFS

|116|[Populating Next Right Pointers in Each Node](https://leetcode.com/problems/populating-next-right-pointers-in-each-node/)|[Solution](../../blob/master/MEDIUM/src/medium/PopulatingNextRightPointersinEachNode.java)| O(n)|O(1) | Medium| BFS

|111|[Minimum Depth of Binary Tree](https://leetcode.com/problems/minimum-depth-of-binary-tree/)|[Solution](../../blob/master/EASY/src/easy/MinimumDepthofBinaryTree.java)| O(n)|O(1)~O(h) | Easy| BFS, DFS

|91|[Decode Ways](https://leetcode.com/problems/decode-ways/)|[Solution](../../blob/master/MEDIUM/src/medium/DecodeWays.java)| O(n)|O(n) | Medium| DP

|98|[Validate Binary Search Tree](https://leetcode.com/problems/validate-binary-search-tree/)|[Solution] | O(n) | O(1) | Medium | DFS/Recursion

|79|[Word Search](https://leetcode.com/problems/word-search/)|[Solution](../../blob/master/MEDIUM/src/medium/WordSearch.java)|O(m*n*l) ? |O(m*n)|Medium|Backtracking/DFS