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Commit2f1856a

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‎README.md

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| # | Title | Solutions | Time | Space | Difficulty | Tag | Notes
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|-----|----------------|---------------|---------------|---------------|-------------|--------------|-----
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|671|[Second Minimum Node In a Binary Tree](https://leetcode.com/problems/second-minimum-node-in-a-binary-tree/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_671.java) | O(n) | O(n) | Easy | Tree, DFS
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|668|[Kth Smallest Number in Multiplication Table](https://leetcode.com/problems/kth-smallest-number-in-multiplication-table/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_668.java) | O(logm*n) | O(1) | Hard | Binary Search
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|667|[Beautiful Arrangement II](https://leetcode.com/problems/beautiful-arrangement-ii/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_667.java) | O(n) | O(1) | Medium | Array
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|666|[Path Sum IV](https://leetcode.com/problems/path-sum-iv/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_666.java) | O(1) | O(1) | Medium | Tree, DFS
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packagecom.fishercoder.solutions;
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importcom.fishercoder.common.classes.TreeNode;
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importjava.util.Iterator;
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importjava.util.Set;
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importjava.util.TreeSet;
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/**
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* 671. Second Minimum Node In a Binary Tree
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*
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* Given a non-empty special binary tree consisting of nodes with the non-negative value,
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* where each node in this tree has exactly two or zero sub-node.
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* If the node has two sub-nodes, then this node's value is the smaller value among its two sub-nodes.
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* Given such a binary tree, you need to output the second minimum value in the set made of all the nodes' value in the whole tree.
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* If no such second minimum value exists, output -1 instead.
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Example 1:
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Input:
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2
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/ \
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2 5
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/ \
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5 7
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Output: 5
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Explanation: The smallest value is 2, the second smallest value is 5.
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Example 2:
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Input:
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2
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/ \
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2 2
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Output: -1
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Explanation: The smallest value is 2, but there isn't any second smallest value.
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*/
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publicclass_671 {
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publicstaticclassSolution1 {
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publicintfindSecondMinimumValue(TreeNoderoot) {
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if (root ==null) {
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return -1;
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}
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Set<Integer>set =newTreeSet<>();
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dfs(root,set);
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Iterator<Integer>iterator =set.iterator();
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intcount =0;
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while (iterator.hasNext()) {
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count++;
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intresult =iterator.next();
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if (count ==2) {
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returnresult;
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}
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}
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return -1;
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}
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privatevoiddfs(TreeNoderoot,Set<Integer>set) {
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if (root ==null) {
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return;
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}
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set.add(root.val);
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dfs(root.left,set);
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dfs(root.right,set);
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return;
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}
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}
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}
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packagecom.fishercoder;
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importcom.fishercoder.common.classes.TreeNode;
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importcom.fishercoder.common.utils.TreeUtils;
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importcom.fishercoder.solutions._671;
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importorg.junit.BeforeClass;
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importorg.junit.Test;
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importjava.util.Arrays;
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importstaticorg.junit.Assert.assertEquals;
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publicclass_671Test {
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privatestatic_671.Solution1solution1;
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privatestaticTreeNoderoot;
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@BeforeClass
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publicstaticvoidsetup() {
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solution1 =new_671.Solution1();
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}
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@Test
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publicvoidtest1() {
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root =TreeUtils.constructBinaryTree(Arrays.asList(2,2,5,null,null,5,7));
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assertEquals(5,solution1.findSecondMinimumValue(root));
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}
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@Test
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publicvoidtest2() {
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root =TreeUtils.constructBinaryTree(Arrays.asList(2,2,2));
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assertEquals(-1,solution1.findSecondMinimumValue(root));
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}
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}

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