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Commit fd38e9e

Browse files
Merge pull request doocs#258 from HendSame/master
add solution 301(d),507(s),508(m),513(m)
2 parents ebda970 + 9369854 commit fd38e9e

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4 files changed

+165
-0
lines changed

4 files changed

+165
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lines changed
Lines changed: 79 additions & 0 deletions
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class Solution {
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public List<String> removeInvalidParentheses(String s) {
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// 最终结果去重
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HashSet<String> set = new HashSet<>();
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// 先遍历一遍,比对,找出需要删除的"("和")"的个数
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// 当前处理字符的位置
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int index = 0;
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// 需要删除"("的个数
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int leftToDelete = 0;
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// 需要删除")"的个数
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int rightToDelete = 0;
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// 剩余几个"("没有匹配到")"
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int leftCount = 0;
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char[] chars = s.toCharArray();
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for (char c : chars) {
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switch (c) {
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case '(':
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leftToDelete++;
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break;
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case ')':
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if (leftToDelete > 0) {
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// 抵消
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leftToDelete--;
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} else {
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rightToDelete++;
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}
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break;
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default:
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}
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}
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dfs(s, index, leftCount, leftToDelete, rightToDelete, set, new StringBuilder());
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ArrayList<String> list = new ArrayList<>();
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list.addAll(set);
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return list;
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}
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private void dfs(String s, int index, int leftCount, int leftToDelete, int rightToDelete, HashSet<String> set, StringBuilder sb) {
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if (index == s.length()) {
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if (leftToDelete == 0 && rightToDelete == 0 && leftCount == 0) {
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set.add(sb.toString());
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}
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return;
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}
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char c = s.charAt(index);
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if (c == '(') {
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// 如果是'(',那么要么删除,要么保留.
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// 如果删除
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if (leftToDelete > 0) {
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StringBuilder tmp = new StringBuilder(sb);
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dfs(s, index + 1, leftCount, leftToDelete - 1, rightToDelete, set, tmp);
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}
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// 不删,或者没有可以删除的
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StringBuilder tmp = new StringBuilder(sb);
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tmp.append(c);
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dfs(s, index + 1, leftCount + 1, leftToDelete, rightToDelete, set, tmp);
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} else if (c == ')') {
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// 删除
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if (rightToDelete > 0) {
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StringBuilder tmp = new StringBuilder(sb);
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dfs(s, index + 1, leftCount, leftToDelete, rightToDelete - 1, set, tmp);
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}
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// 在前面有'('的时候保留.
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if (leftCount > 0) {
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StringBuilder tmp = new StringBuilder(sb);
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tmp.append(c);
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dfs(s, index + 1, leftCount - 1, leftToDelete, rightToDelete, set, tmp);
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} else {
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// ")"这个没有"("和他对应,结束
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return;
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}
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} else {
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// 其他字符
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StringBuilder tmp = new StringBuilder(sb);
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tmp.append(c);
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dfs(s, index + 1, leftCount, leftToDelete, rightToDelete, set, tmp);
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}
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}
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}
Lines changed: 14 additions & 0 deletions
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public class Solution {
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public boolean checkPerfectNumber(int num) {
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if (num == 0 || num == 1) {
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return false;
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}
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int sum = 1;
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for (int i = 2; i <= Math.sqrt(num); i++) {
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if (num % i == 0) {
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sum = sum + i + num / i;
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}
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}
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return num == sum;
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}
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}
Lines changed: 41 additions & 0 deletions
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/**
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* Definition for a binary tree node.
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* public class TreeNode {
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* int val;
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* TreeNode left;
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* TreeNode right;
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* TreeNode(int x) { val = x; }
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* }
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*/
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public class Solution {
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// 后续遍历,遍历的同时,找最大值和计算次数
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Map<Integer, Integer> map = new HashMap<>();
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int max = Integer.MIN_VALUE;
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public int[] findFrequentTreeSum(TreeNode root) {
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if (root == null) {
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return new int[0];
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}
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dfs(root);
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List<Integer> list = map.entrySet().stream()
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.filter(m -> m.getValue() == max).map(i -> i.getKey()).collect(Collectors.toList());
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int[] res = new int[list.size()];
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for (int i = 0; i < list.size(); i++) {
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res[i] = list.get(i);
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}
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return res;
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}
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private int dfs(TreeNode root) {
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if (root == null) {
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return 0;
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}
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int left = dfs(root.left);
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int right = dfs(root.right);
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int sum = root.val + left + right;
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int current = map.getOrDefault(sum, 0) + 1;
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map.put(sum, current);
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max = Math.max(current, max);
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return sum;
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}
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}
Lines changed: 31 additions & 0 deletions
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/**
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* Definition for a binary tree node.
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* public class TreeNode {
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* int val;
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* TreeNode left;
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* TreeNode right;
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* TreeNode(int x) { val = x; }
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* }
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*/
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class Solution {
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int max = -1;
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int value = 0;
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public int findBottomLeftValue(TreeNode root) {
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dfs(root, 0);
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return value;
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}
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private void dfs(TreeNode root, int d) {
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if (root == null) {
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return;
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}
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d++;
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if (max < d) {
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max = d;
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value = root.val;
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}
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dfs(root.left, d);
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dfs(root.right, d);
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}
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}

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