6180. 最小偶倍数 - 力扣（LeetCode）
sb题目
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| class Solution {
public int smallestEvenMultiple(int n) {
return n%2==0?n:n*2;
}
}
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6181. 最长的字母序连续子字符串的长度 - 力扣（LeetCode）
单指针直接遍历计数就好了
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| class Solution {
public int longestContinuousSubstring(String s) {
char lastC = 0;
int len = 0;
int res = 0;
for (int i = 0; i < s.length();i++) {
char c = s.charAt(i);
if (c != lastC + 1) {
res = Math.max(len, res);
len = 1;
} else {
len++;
}
lastC = c;
}
res = Math.max(len, res);
return res;
}
}
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6182. 反转二叉树的奇数层 - 力扣（LeetCode）
先后序dfs记录每个点在哪个层，放进一个list
然后按层遍历哪些list，把他们的值返回来重新存放即可
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|
class Solution {
public TreeNode reverseOddLevels(TreeNode root) {
Map<Integer, List<TreeNode>> nodes = new HashMap<>();
dfs(root, 0, nodes);
for (Map.Entry<Integer, List<TreeNode>> entry : nodes.entrySet()) {
if (entry.getKey() % 2 == 0) {
continue;
}
List<TreeNode> list = entry.getValue();
List<Integer> valus = list.stream().map(tn -> tn.val).collect(Collectors.toList());
Collections.reverse(valus);
for (int i = 0; i < list.size();i++) {
list.get(i).val = valus.get(i);
}
}
return root;
}
void dfs(TreeNode node, int level, Map<Integer, List<TreeNode>> map) {
if( node == null) {
return ;
}
dfs(node.left, level+1, map);
dfs(node.right, level+1, map);
if (!map.containsKey(level)) {
map.put(level, new ArrayList<>());
}
map.get(level).add(node);
}
}
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6183. 字符串的前缀分数和 - 力扣（LeetCode）
字段树，只有1000的范围，不会超，直接构建完树后直接遍历
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| class Solution {
static class Node {
int count = 0;
Node[] nextNodes = new Node[26];
}
public int[] sumPrefixScores(String[] words) {
Node root = new Node();
for (String word : words) {
Node node = root;
for (char c : word.toCharArray()) {
if (node.nextNodes[c-'a'] == null) {
node.nextNodes[c-'a'] = new Node();
}
node.nextNodes[c-'a'].count++;
node = node.nextNodes[c-'a'];
}
}
int[] res = new int[words.length];
int i = 0;
for (String word : words) {
Node node = root;
int sum = 0;
for (char c : word.toCharArray()) {
if (node.nextNodes[c-'a'] != null) {
sum += node.nextNodes[c - 'a'].count;
}
node = node.nextNodes[c-'a'];
}
res[i++] = sum;
}
return res;
}
}
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