Leetcode 简单
Leetcode
- [504. 七进制数](https://leetcode-cn.com/problems/base-7/)
- [521. 最长特殊序列 Ⅰ](https://leetcode-cn.com/problems/longest-uncommon-subsequence-i/)
- [258. 各位相加](https://leetcode-cn.com/problems/add-digits/)
- [★2016. 增量元素之间的最大差值](https://leetcode-cn.com/problems/maximum-difference-between-increasing-elements/)
- [2016. 增量元素之间的最大差值](https://leetcode-cn.com/problems/maximum-difference-between-increasing-elements/)
- [★917. 仅仅反转字母](https://leetcode-cn.com/problems/reverse-only-letters/)
- [717. 1比特与2比特字符](https://leetcode-cn.com/problems/1-bit-and-2-bit-characters/)
- [1791. 找出星型图的中心节点](https://leetcode-cn.com/problems/find-center-of-star-graph/)
- [1380. 矩阵中的幸运数](https://leetcode-cn.com/problems/lucky-numbers-in-a-matrix/)
- [1342. 将数字变成 0 的操作次数](https://leetcode-cn.com/problems/number-of-steps-to-reduce-a-number-to-zero/)
- [1763. 最长的美好子字符串](https://leetcode-cn.com/problems/longest-nice-substring/)
- [2047. 句子中的有效单词数](https://leetcode-cn.com/problems/number-of-valid-words-in-a-sentence/)
- [2000. 反转单词前缀](https://leetcode-cn.com/problems/reverse-prefix-of-word/)
- [2006. 差的绝对值为 K 的数对数目](https://leetcode-cn.com/problems/count-number-of-pairs-with-absolute-difference-k/)
- [1189. “气球” 的最大数量](https://leetcode-cn.com/problems/maximum-number-of-balloons/)
- [1725. 可以形成最大正方形的矩形数目](https://leetcode-cn.com/problems/number-of-rectangles-that-can-form-the-largest-square/)
- [1984. 学生分数的最小差值](https://leetcode-cn.com/problems/minimum-difference-between-highest-and-lowest-of-k-scores/)
- [1748. 唯一元素的和](https://leetcode-cn.com/problems/sum-of-unique-elements/)
504. 七进制数
class Solution:
def convertToBase7(self, num: int) -> str:
if num == 0: return "0"
negative = num < 0
num = abs(num)
digits = []
while num:
num, r = divmod(num, 7)
digits.append(str(r))
if negative: digits.append('-')
return ''.join(reversed(digits))
521. 最长特殊序列 Ⅰ
class Solution:
def findLUSlength(self, a: str, b: str) -> int:
m, n = len(a), len(b)
if m != n: return max(m, n)
else: return -1 if a == b else m
258. 各位相加
class Solution:
def addDigits(self, num: int) -> int:
while num > 9: # 个位数字
rem = 0 # 记各位的和
while num:
rem += num % 10
num //= 10
num = rem
return num
class Solution {
public int addDigits(int num) {
while (num > 9){
int rem = 0;
while (num != 0){
rem += num % 10;
num /= 10;
}
num = rem;
}
return num;
}
}
★2016. 增量元素之间的最大差值
class Solution:
def maximumDifference(self, nums: List[int]) -> int:
# res, n = -1, len(nums)
# for i in range(n):
# for j in range(i+1, n):
# if nums[i] < nums[j]:
# res = max(res, nums[j]-nums[i])
# ★维护一个最小值，从第二个开始，每个元素和最小值比较。
min_, res = nums[0], -1
for x in nums[1:]:
res = max(res, x - min_)
min_ = min(min_, x)
return res or -1
# 加条件会变慢 if nums[j] > nums[i]
# return max(0, max(nums[j] - nums[i] for i in range(len(nums)) for j in range(i+1, len(nums)))) or -1
class Solution {
public int maximumDifference(int[] nums) {
int res = -1, min = nums[0];
// for (int i = 1; i < nums.length; i++){
// int tmp = nums[i] - min;
// res = (tmp > res) ? tmp : res;
// min = (nums[i] < min) ? nums[i] : min;
// }
for (int i : nums){
res = Math.max(res, i - min);
min = Math.min(i, min);
}
return (res == 0) ? -1:res; // 可能有相同元素存在
}
}
2016. 增量元素之间的最大差值
class Solution:
def maximumDifference(self, nums: List[int]) -> int:
res, a = -1, nums[0]
for b in nums[1:]:
if a < b: res = max(res, b - a)
else: a = min(a, b)
return res
class Solution {
public int maximumDifference(int[] nums) {
int res = -1, min = nums[0];
for (int i : nums){
res = Math.max(res, i - min);
min = Math.min(i, min);
}
return (res == 0) ? -1:res; // 可能有相同元素存在
}
}
★917. 仅仅反转字母
class Solution:
def reverseOnlyLetters(self, s: str) -> str:
# x, i, j = list(s), 0, len(s)-1
# while i < j:
# if not x[i].isalpha(): i += 1
# elif not x[j].isalpha(): j -= 1
# else:
# x[i], x[j] = x[j], x[i]
# i += 1
# j -= 1
# return "".join(x)
t, x = [c for c in s if c.isalpha()], []
for c in s:
# if c.isalpha(): x.append(t.pop())
# else: x.append(c)
x.append(t.pop() if c.isalpha() else c)
return "".join(x)
# return ''.join(t.pop if c.isalpha() else c for c in s)
class Solution {
public String reverseOnlyLetters(String s) {
int i = 0, j = s.length() - 1;
char[] t = s.toCharArray();
while (i < j){
if (!Character.isLetter(t[i])) i++;
else if (!Character.isLetter(t[j])) j--;
else {
char tmp =t[i]; t[i] = t[j]; t[j] = tmp;
i++; j--;
}
}
return new String(t);
// StringBuilder sb = new StringBuilder();
// char[] t = s.toCharArray();
// int j = s.length() - 1;
// for (char c : t){
// while (j > 0 && !Character.isLetter(t[j])) j--;
// sb.append(Character.isLetter(c) ? t[j--] : c);
// }
// return sb.toString();
}
}
717. 1比特与2比特字符
遍历，遇到 0 走一步，遇到 1 走两步。
class Solution:
def isOneBitCharacter(self, bits: List[int]) -> bool:
# n = len(bits)
# i = n - 2
# while i >= 0 and bits[i]: i -= 1
# return (n - i) % 2 == 0
i, n = 0, len(bits)
while i < n - 1: i += bits[i] + 1
return i == n - 1
1791. 找出星型图的中心节点
# python
return edges[0][0] if edges[0][0] in edges[1] else edges[0][1]
// java
return (edges[0][0] == edges[1][0] || edges[0][0] == edges[1][1]) ? edges[0][0] : edges[0][1];
}
}
1380. 矩阵中的幸运数
class Solution:
def luckyNumbers (self, matrix: List[List[int]]) -> List[int]:
n = len(matrix[0])
row, col = [0] * n, [0] * n # row[idx]行的最小值在 idx 列，col 列的最大值。
for r in matrix:
tmp, idx = inf, 0 # tmp 为当前行的最小值，对应的列为 idx。
for j, v in enumerate(r):
if v < tmp:
tmp = v
idx = j
col[j] = max(col[j], v)
row[idx] = max(row[idx], tmp) # 但保留最大值。
return [row[i] for i in range(n) if row[i] == col[i]]
# row = [min(row) for row in matrix]
# col = [max(col) for col in zip(*matrix)]
# return [x for i, r in enumerate(matrix) for j, x in enumerate(r) if row[i] == col[j]]
1342. 将数字变成 0 的操作次数
class Solution:
def numberOfSteps(self, num: int) -> int:
n = 0
while num:
num = num - 1 if num % 2 else num // 2
n += 1
return n
class Solution {
public int numberOfSteps(int num) {
int res = 0;
while (num > 0) {
if (num % 2 == 0) num >>= 1;
else num--;
res++;
}
return res;
}
}
1763. 最长的美好子字符串
class Solution:
def longestNiceSubstring(self, s: str) -> str:
# n = len(s)
# maxPos = maxLen = 0
# for i in range(n):
# upp = low = 0
# for j in range(i, n):
# if s[j].islower(): low |= 1 << (ord(s[j]) - ord('a'))
# else: upp |= 1 << (ord(s[j]) - ord('A'))
# if upp == low and j - i + 1 > maxLen:
# maxPos, maxLen = i, j - i + 1
# return s[maxPos: maxPos + maxLen]
def f(s):
w = set(s)
for c in w:
if c.swapcase() not in w: break
else:
res.append(s)
return
for t in s.split(c):
if t: f(t)
res = ['']
f(s)
res.sort(key=lambda x : -len(x))
return res[0]
def f(s):
# global x # Leetcode 不通过
nonlocal x # Jupyterlab 不通过
w = set(s)
for c in w:
if c.swapcase() not in w: break;
else:
if len(s) > len(x):
x = s
return
for t in s.split(c):
if t: f(t)
x = ''
f(s)
return x
class Solution {
public String longestNiceSubstring(String s) {
int start = 0, end = 0;
for (int i = 0; i < s.length(); i++){
int lower = 0, upper = 0;
for (int j = i; j < s.length(); j++){
char c = s.charAt(j);
if (c > 96) lower |= 1 << c - 'a';
if (c < 96) upper |= 1 << c - 'A';
if (lower == upper && j + 1 - i > end - start){
start = i;
end = j + 1;
}
}
}
return s.substring(start, end);
}
}
2047. 句子中的有效单词数
class Solution:
def countValidWords(self, sentence: str) -> int:
# res = 0
# words = sentence.split()
# for word in words:
# if word in ['!', '.', ',']:
# res += 1
# continue
# if word[-1] in '!.,':
# word = word[:-1]
# if word[0] != '-' and word[-1] != '-':
# w = word.split('-')
# if len(w) <= 2 and all(x.isalpha() for x in w):
# res += 1
# return res
#regex = r'[a-z]*([a-z]-[a-z]+)?[!.,]?$'
regex = r"^([,.!]|[a-z]+(-[a-z]+)?[,.!]?)$"
return sum(bool(re.match(regex, word)) for word in sentence.split())
class Solution {
public int countValidWords(String sentence) {
int res = 0;
// String regex = "^([,.!]|[a-z]+(-[a-z]+)?[,.!]?)$";
for (String s : sentence.split(" +")) {
// if (s.matches(regex)) res++;
if (check(s)) res++;
}
return res;
}
public boolean check(String word) {
if (word == "") return false;
int n = word.length();
boolean hyphen = false;
for (int i = 0; i < n; i++) {
if (Character.isDigit(word.charAt(i))) {
return false;
} else if (word.charAt(i) == '-') {
if (hyphen == true || i == 0 || i == n - 1 || !Character.isLetter(word.charAt(i - 1)) || !Character.isLetter(word.charAt(i + 1))) {
return false;
}
hyphen = true;
} else if ((word.charAt(i) == '!' || word.charAt(i) == '.' || word.charAt(i) == ',') && (i != n - 1)) {
return false;
}
}
return true;
}
}
2000. 反转单词前缀
class Solution:
def reversePrefix(self, word: str, ch: str) -> str:
idx = word.find(ch) + 1
return word[:idx][::-1] + word[idx:] if idx != 0 else word
class Solution {
public String reversePrefix(String word, char ch) {
char[] arr = word.toCharArray();
for (int i = 0, j = word.indexOf(ch); i < j; i++, j--){
char tmp = arr[i];
arr[i] = arr[j];
arr[j] = tmp;
}
return new String(arr);
}
}
2006. 差的绝对值为 K 的数对数目
class Solution:
def countKDifference(self, nums: List[int], k: int) -> int:
# 方法一：
# res, n = 0, len(nums)
# for i in range(n):
# for j in range(i+1, n):
# if abs(nums[i]-nums[j]) == k:
# res += 1
# return res
# 方法二：哈希表
# res, d = 0, defaultdict(int)
# for i in nums:
# d[k+i] += 1
# # for i in nums:
# # res += d[i]
# return sum(d[i] for i in nums)
# 方法三：Counter
# res, c = 0, Counter()
# for i in nums:
# res += c[i + k] + c[i - k]
# c[i] += 1
# return res
c = Counter(nums)
return sum(c[i + k] for i in nums)
class Solution {
public int countKDifference(int[] nums, int k) {
int[] c = new int[200];
int ans = 0;
for (int num : nums){
ans += c[num + k] + (num >= k ? c[num - k] : 0);
c[num]++;
// c[num + k]++;
// if (num >= k) c[num - k]++;
// ans += c[num];
}
return ans;
}
}
1189. “气球” 的最大数量
class Solution:
def maxNumberOfBalloons(self, text: str) -> int:
# d = {c: 0 for c in 'balon'}
# for c in text:
# if c in 'balon': d[c] += 1
# return min(d[c]//2 if c in 'ol' else d[c] for c in d)
c = Counter(x for x in text if x in 'balon')
c['l'] //= 2
c['o'] //= 2
return min(c.values()) if len(c) == 5 else 0
class Solution {
public int maxNumberOfBalloons(String text) {
int[] cnt = new int[5];
// for (char ch : text.toCharArray()){
// if (ch == 'a') cnt[0]++;
// if (ch == 'b') cnt[1]++;
// if (ch == 'l') cnt[2]++;
// if (ch == 'o') cnt[3]++;
// if (ch == 'n') cnt[4]++;
// }
for(int i = 0; i < text.length(); i++) {
switch(text.charAt(i)){
case 'a': cnt[0]++; break;
case 'b': cnt[1]++; break;
case 'l': cnt[2]++; break;
case 'o': cnt[3]++; break;
case 'n': cnt[4]++; //break;
// default: continue;
}
}
cnt[2] /= 2;
cnt[3] /= 2;
// return Arrays.stream(cnt).min().getAsInt();
int ans = cnt[0];
for (int i = 0; i < 5; i++) ans = Math.min(ans, cnt[i]);
return ans;
}
}
1725. 可以形成最大正方形的矩形数目
class Solution:
def countGoodRectangles(self, rectangles: List[List[int]]) -> int:
res = maxLen = 0
for h, w in rectangles:
minLen = min(h, w)
if maxLen == minLen: res += 1
elif maxLen < minLen:
maxLen = minLen
res = 1
return res
class Solution {
public int countGoodRectangles(int[][] rectangles) {
int res = 0, max = 0;
for (int[] rec : rectangles){
int min = Math.min(rec[0], rec[1]);
if (max == min) res++;
else if (max < min){
max = min;
res = 1;
}
}
return res;
}
}
1984. 学生分数的最小差值
class Solution:
def minimumDifference(self, nums: List[int], k: int) -> int:
# 排序 滑动窗口
nums.sort()
res = inf
for i in range(len(nums) - k + 1):
res = min(res, nums[i + k - 1]-nums[i])
return res
class Solution {
public int minimumDifference(int[] nums, int k) {
Arrays.sort(nums);
int res = Integer.MAX_VALUE;
for (int i = 0; i < nums.length - k + 1; i++){
int tmp = nums[i+k-1] - nums[i];
res = (tmp < res) ? tmp:res;
}
return res;
}
}
1748. 唯一元素的和
class Solution:
def sumOfUnique(self, nums: List[int]) -> int:
res = {}
for i in nums:
res[i] = res.get(i, 0) + 1
return sum(x for x in res if res[x] == 1)
res, ans = {}, 0
for i in nums:
if i in res:
if res[i] == 1: ans -= i
res[i] = 2
else:
res[i] = 1
ans += i
return ans
class Solution {
public int sumOfUnique(int[] nums) {
Map<Integer, Integer> map = new HashMap<>();
int res = 0;
// for (int num : nums){
// map.put(num, map.getOrDefault(num, 0) + 1);
// }
// for (Map.Entry entry : map.entrySet()) {
// if (entry.getValue() == 1) res += entry.getKey();
// }
for (int num : nums) {
if (!map.containsKey(num)) {
res += num; // 先加上
map.put(num, 1);
} else if (map.get(num) == 1) {
res -= num; // 多个减一次
map.put(num, 2);
}
}
return res;
}
}
class Solution {
public int sumOfUnique(int[] nums) {
Arrays.sort(nums);
int n = nums.length, ans = 0, start = 0;
for (int i = 1; i < n; i++) {
if (nums[start] != nums[i]){
if (i - start == 1) ans += nums[start];
start = i;
}
}
if (n - start == 1) ans += nums[n - 1];
return ans;
}
}