From eb428505957c21e8f2bb27573f2f946d58249c9e Mon Sep 17 00:00:00 2001 From: liu13 <1099976891@qq.com> Date: Wed, 15 May 2019 13:42:10 +0800 Subject: [PATCH] 20190515 --- code/lc559.java | 36 ++++++++++++++++++++++++++++ code/lc589.java | 41 +++++++++++++++++++++++++++++++ code/lc590.java | 33 +++++++++++++++++++++++++ code/lc834.java | 64 +++++++++++++++++++++++++++++++++++++++++++++++++ readme.md | 4 ++++ 5 files changed, 178 insertions(+) create mode 100644 code/lc559.java create mode 100644 code/lc589.java create mode 100644 code/lc590.java create mode 100644 code/lc834.java diff --git a/code/lc559.java b/code/lc559.java new file mode 100644 index 0000000..6518be1 --- /dev/null +++ b/code/lc559.java @@ -0,0 +1,36 @@ +package code; + +import java.util.List; + +/* + * 559. Maximum Depth of N-ary Tree + * 题意：多叉树的最大深度 + * 难度：Easy + * 分类：Tree, Depth-first Search, Breadth-first Search + * 思路：BFS 也能做和 lc104思路一样 + * Tips：lc104, lc111 + */ + +public class lc559 { + class Node { + public int val; + public List children; + + public Node() {} + + public Node(int _val,List _children) { + val = _val; + children = _children; + } + } + + public int maxDepth(Node root) { + if(root==null) return 0; + int res = 0; + for (Node nd : root.children) { + res = Math.max(maxDepth(nd), res); + } + return res+1; + } + +} diff --git a/code/lc589.java b/code/lc589.java new file mode 100644 index 0000000..1b8efc8 --- /dev/null +++ b/code/lc589.java @@ -0,0 +1,41 @@ +package code; + +import java.util.ArrayList; +import java.util.List; + +/* + * 589. N-ary Tree Preorder Traversal + * 题意：多叉树先序遍历 + * 难度：Easy + * 分类：Tree + * 思路： + * Tips： + */ +public class lc589 { + class Node { + public int val; + public List children; + + public Node() {} + + public Node(int _val,List _children) { + val = _val; + children = _children; + } + } + + List res; + public List preorder(Node root) { + res = new ArrayList<>(); + helper(root); + return res; + } + + public void helper(Node root){ + if(root==null) return; + res.add(root.val); + for(Node nd:root.children){ + helper(nd); + } + } +} diff --git a/code/lc590.java b/code/lc590.java new file mode 100644 index 0000000..20bf045 --- /dev/null +++ b/code/lc590.java @@ -0,0 +1,33 @@ +package code; + +import java.util.ArrayList; +import java.util.List; + +public class lc590 { + class Node { + public int val; + public List children; + + public Node() {} + + public Node(int _val,List _children) { + val = _val; + children = _children; + } + } + + List res; + public List postorder(Node root) { + res = new ArrayList<>(); + helper(root); + return res; + } + + public void helper(Node root){ + if(root==null) return; + for(Node nd:root.children){ + helper(nd); + } + res.add(root.val); + } +} diff --git a/code/lc834.java b/code/lc834.java new file mode 100644 index 0000000..f070402 --- /dev/null +++ b/code/lc834.java @@ -0,0 +1,64 @@ +package code; + +import java.util.HashMap; +import java.util.HashSet; +/* + * 834. Sum of Distances in Tree + * 题意：求树中每个节点的值，到其他节点的距离和 + * 难度：Hard + * 分类：Tree, Depth-first Search + * 思路：真的难，我是做不出来 + * 两次遍历，第一次后续遍历，计算出每个节点为根的树，有几个孩子节点，并计算出root的结果 + * 根据前一步的计算结果，开始先序遍历，一步步计算出其他节点的结果 + * res[node] = res[parent]-2*count[node]+count.length; + * https://leetcode.com/problems/sum-of-distances-in-tree/discuss/130583/C%2B%2BJavaPython-Pre-order-and-Post-order-DFS-O(N) + * https://leetcode.com/problems/sum-of-distances-in-tree/discuss/130567/Two-traversals-O(N)-python-solution-with-Explanation + * Tips： + */ +public class lc834 { + public static void main(String[] args) { + int[][] arr = {{0,1},{0,2},{2,3},{2,4},{2,5}}; + sumOfDistancesInTree(6, arr); + } + + static int[] count; + static int[] res; + static HashMap> hm = new HashMap(); + public static int[] sumOfDistancesInTree(int N, int[][] edges) { + if(edges.length==0) return new int[]{0}; + count = new int[N]; //记录n为跟的树，下边有多少个节点 + res = new int[N]; + for (int i = 0; i < edges.length ; i++) { //双向都添加，遍历的时候判断一下，因为并不一定0就是根 + HashSet hs = hm.getOrDefault(edges[i][0], new HashSet()); + hs.add(edges[i][1]); + hm.put(edges[i][0], hs); + hs = hm.getOrDefault(edges[i][1], new HashSet()); + hs.add(edges[i][0]); + hm.put(edges[i][1], hs); + } + helper1(0, -1); + helper2(0, -1); + return res; + } + + public static int helper1(int node, int parent){ //后序遍历，求root对应的结果，计算每个节点的count + HashSet hs = hm.getOrDefault(node, new HashSet()); + for (Integer i:hs) { + if(i==parent) continue; //是parent的话直接略过 + count[node] += helper1(i, node); + res[node] += res[i] + count[i]; + } + count[node]++; + return count[node]; + } + + public static void helper2(int node, int parent){ //先序遍历，求结果 + HashSet hs = hm.getOrDefault(node, new HashSet()); + if(node!=0) + res[node] = res[parent]-2*count[node]+count.length; //转移计算 + for (Integer i:hs) { + if(i==parent) continue; //是parent的话直接略过 + helper2(i, node); + } + } +} diff --git a/readme.md b/readme.md index cddca84..8d4be9c 100644 --- a/readme.md +++ b/readme.md @@ -212,9 +212,12 @@ LeetCode 指南 | 494 [Java](./code/lc494.java) | 538 [Java](./code/lc538.java) | 543 [Java](./code/lc543.java) +| 559 [Java](./code/lc559.java) | 560 [Java](./code/lc543.java) | 572 [Java](./code/lc572.java) | 581 [Java](./code/lc581.java) +| 589 [Java](./code/lc589.java) +| 590 [Java](./code/lc590.java) | 617 [Java](./code/lc617.java) | 621 [Java](./code/lc621.java) | 647 [Java](./code/lc647.java) @@ -222,6 +225,7 @@ LeetCode 指南 | 714 [Java](./code/lc714.java) | 746 [Java](./code/lc746.java) | 771 [Java](./code/lc771.java) +| 834 [Java](./code/lc834.java) | 877 [Java](./code/lc877.java) | 921 [Java](./code/lc921.java) | 922 [Java](./code/lc922.java) -- GitLab