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Commit 4e09d85

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19 files changed

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19 files changed

+322
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‎codeforces/codeforces-19/src/main/java/p1842/CF1842C.java

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Original file line numberDiff line numberDiff line change
@@ -48,6 +48,7 @@ private static String solve() {
4848
C. Tenzing and Balls
4949
https://codeforces.com/contest/1842/problem/C
5050
51+
灵茶の试炼 2024年12月17日
5152
题目大意:
5253
Tenzing 有 n 个球排成一行。左边第 i 个球的颜色是 ai。
5354
Tenzing 可以任意次数做以下操作:

‎codeforces/codeforces-19/src/main/java/p1878/CF1878E.java

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Original file line numberDiff line numberDiff line change
@@ -78,6 +78,7 @@ static boolean checkMid(int l, int k, int mid) {
7878
E. Iva & Pav
7979
https://codeforces.com/contest/1878/problem/E
8080
81+
灵茶の试炼 2025年02月04日
8182
题目大意:
8283
Iva 和 Pav 是一对著名的塞尔维亚竞技编程夫妇。在塞尔维亚,人们称帕夫为"帕普卡",这就是为什么他会让伊娃的所有愿望都实现。
8384
Iva 给了 Pav 一个 n 个元素的数组 a。

‎codeforces/codeforces-20/src/main/java/p1932/CF1932C.java

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Original file line numberDiff line numberDiff line change
@@ -47,6 +47,7 @@ private static String solve() {
4747
C. LR-remainders
4848
https://codeforces.com/contest/1932/problem/C
4949
50+
灵茶の试炼 2025年01月28日
5051
题目大意:
5152
给定一个长度为 n 的数组 a,一个正整数 m,以及一串长度为 n 的命令。每个命令都是字符"L"或字符"R"。
5253
按照在字符串 s 中写入的顺序处理所有 n 个命令。命令的处理方法如下:

‎leetcode/leetcode-01/src/main/java/Solution12.java

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -3,19 +3,19 @@ public class Solution12 {
33
private static final String[] SYMBOLS = {"M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I"};
44

55
public String intToRoman(int num) {
6-
StringBuilder stringBuilder = new StringBuilder();
6+
StringBuilder ans = new StringBuilder();
77
for (int i = 0; i < VALUES.length; i++) {
88
int value = VALUES[i];
99
String symbol = SYMBOLS[i];
1010
while (num - value >= 0) {
1111
num -= value;
12-
stringBuilder.append(symbol);
12+
ans.append(symbol);
1313
}
1414
if (num == 0) {
1515
break;
1616
}
1717
}
18-
return stringBuilder.toString();
18+
return ans.toString();
1919
}
2020
}
2121
/*
Lines changed: 53 additions & 15 deletions
Original file line numberDiff line numberDiff line change
@@ -1,24 +1,63 @@
1+
import java.util.ArrayList;
2+
import java.util.Arrays;
3+
import java.util.Comparator;
4+
import java.util.List;
5+
16
public class Solution1534 {
7+
// O(n^3)
28
public int countGoodTriplets(int[] arr, int a, int b, int c) {
3-
int len = arr.length;
4-
int cnt = 0;
5-
for (int i = 0; i < len; i++) {
6-
for (int j = i + 1; j < len; j++) {
7-
if ((Math.abs(arr[i] - arr[j]) <= a)) {
8-
cnt = getCnt(arr, b, c, len, cnt, i, j);
9+
int n = arr.length;
10+
int ans = 0;
11+
for (int i = 0; i < n; i++) {
12+
for (int j = i + 1; j < n; j++) {
13+
if ((Math.abs(arr[i] - arr[j]) > a)) continue;
14+
for (int k = j + 1; k < n; k++) {
15+
if ((Math.abs(arr[j] - arr[k]) <= b) && (Math.abs(arr[i] - arr[k]) <= c)) {
16+
ans++;
17+
}
918
}
1019
}
1120
}
12-
return cnt;
21+
return ans;
1322
}
1423

15-
private int getCnt(int[] arr, int b, int c, int len, int cnt, int i, int j) {
16-
for (int k = j + 1; k < len; k++) {
17-
if ((Math.abs(arr[j] - arr[k]) <= b) && (Math.abs(arr[i] - arr[k]) <= c)) {
18-
cnt++;
24+
// O(n^2)
25+
public int countGoodTriplets2(int[] arr, int a, int b, int c) {
26+
int n = arr.length;
27+
Integer[] ids = new Integer[n];
28+
for (int i = 0; i < n; i++) ids[i] = i;
29+
Arrays.sort(ids, Comparator.comparingInt(o -> arr[o]));
30+
31+
int ans = 0;
32+
for (int j : ids) {
33+
int y = arr[j];
34+
List<Integer> left = new ArrayList<>();
35+
for (int i : ids) {
36+
if (i < j && Math.abs(arr[i] - y) <= a) {
37+
left.add(arr[i]);
38+
}
39+
}
40+
41+
List<Integer> right = new ArrayList<>();
42+
for (int k : ids) {
43+
if (k > j && Math.abs(arr[k] - y) <= b) {
44+
right.add(arr[k]);
45+
}
46+
}
47+
48+
int k1 = 0;
49+
int k2 = 0;
50+
for (int x : left) {
51+
while (k2 < right.size() && right.get(k2) <= x + c) {
52+
k2++;
53+
}
54+
while (k1 < right.size() && right.get(k1) < x - c) {
55+
k1++;
56+
}
57+
ans += k2 - k1;
1958
}
2059
}
21-
return cnt;
60+
return ans;
2261
}
2362
}
2463
/*
@@ -40,7 +79,6 @@ private int getCnt(int[] arr, int b, int c, int len, int cnt, int i, int j) {
4079
0 <= arr[i] <= 1000
4180
0 <= a, b, c <= 1000
4281
43-
暴力枚举即可。时间复杂度 O(n^3)
44-
可以进行剪枝,时间复杂度 O(n^2)
45-
抽取方法避免嵌套过深。
82+
暴力枚举 / 前缀和 / 排序+三指针
83+
https://leetcode.cn/problems/count-good-triplets/solutions/3622921/liang-chong-fang-fa-bao-li-mei-ju-qian-z-apcv/
4684
*/

‎leetcode/leetcode-16/src/test/java/Solution1534Tests.java

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Original file line numberDiff line numberDiff line change
@@ -12,6 +12,7 @@ public void example1() {
1212
int c = 3;
1313
int expected = 4;
1414
Assertions.assertEquals(expected, solution1534.countGoodTriplets(arr, a, b, c));
15+
Assertions.assertEquals(expected, solution1534.countGoodTriplets2(arr, a, b, c));
1516
}
1617

1718
@Test
@@ -22,5 +23,6 @@ public void example2() {
2223
int c = 1;
2324
int expected = 0;
2425
Assertions.assertEquals(expected, solution1534.countGoodTriplets(arr, a, b, c));
26+
Assertions.assertEquals(expected, solution1534.countGoodTriplets2(arr, a, b, c));
2527
}
2628
}

‎leetcode/leetcode-19/src/main/java/Solution1863.java

Lines changed: 10 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -38,6 +38,16 @@ private void helper(int[] nums, int idx, LinkedList<Integer> subset, List<List<I
3838
subset.removeLast();
3939
}
4040
}
41+
42+
// O(n)
43+
public int subsetXORSum2(int[] nums) {
44+
int n = nums.length;
45+
int or = 0;
46+
for (int x : nums) {
47+
or |= x;
48+
}
49+
return or << (n - 1);
50+
}
4151
}
4252
/*
4353
1863. 找出所有子集的异或总和再求和

‎leetcode/leetcode-19/src/test/java/Solution1863Tests.java

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@@ -9,19 +9,22 @@ public void example1() {
99
int[] nums = {1, 3};
1010
int expected = 6;
1111
Assertions.assertEquals(expected, solution1863.subsetXORSum(nums));
12+
Assertions.assertEquals(expected, solution1863.subsetXORSum2(nums));
1213
}
1314

1415
@Test
1516
public void example2() {
1617
int[] nums = {5, 1, 6};
1718
int expected = 28;
1819
Assertions.assertEquals(expected, solution1863.subsetXORSum(nums));
20+
Assertions.assertEquals(expected, solution1863.subsetXORSum2(nums));
1921
}
2022

2123
@Test
2224
public void example3() {
2325
int[] nums = {3, 4, 5, 6, 7, 8};
2426
int expected = 480;
2527
Assertions.assertEquals(expected, solution1863.subsetXORSum(nums));
28+
Assertions.assertEquals(expected, solution1863.subsetXORSum2(nums));
2629
}
2730
}

‎leetcode/leetcode-21/src/main/java/Solution2075.java

Lines changed: 6 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -1,26 +1,25 @@
11
public class Solution2075 {
22
public String decodeCiphertext(String encodedText, int rows) {
3-
int len = encodedText.length();
4-
int cols = len / rows;
3+
int cols = encodedText.length() / rows;
54
// 还原矩阵
6-
char[][] chars = new char[rows][cols];
5+
char[][] grid = new char[rows][cols];
76
int idx = 0;
87
for (int i = 0; i < rows; i++) {
98
for (int j = 0; j < cols; j++) {
10-
chars[i][j] = encodedText.charAt(idx++);
9+
grid[i][j] = encodedText.charAt(idx++);
1110
}
1211
}
1312
// 还原 originalText
14-
StringBuilder stringBuilder = new StringBuilder();
13+
StringBuilder ans = new StringBuilder();
1514
for (int i = 0; i < cols; i++) {
1615
for (int j = 0; j < rows; j++) {
1716
if (j + i < cols) {
18-
stringBuilder.append(chars[j][j + i]);
17+
ans.append(grid[j][j + i]);
1918
}
2019
}
2120
}
2221
// 移除 尾随空格
23-
return stringBuilder.toString().stripTrailing();
22+
return ans.toString().stripTrailing();
2423
}
2524
}
2625
/*
Lines changed: 8 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -1,18 +1,13 @@
11
public class Solution2109 {
22
public String addSpaces(String s, int[] spaces) {
3-
int first = spaces[0];
4-
int last = spaces[spaces.length - 1];
5-
StringBuilder stringBuilder = new StringBuilder();
6-
7-
// first
8-
stringBuilder.append(s, 0, first).append(" ");
9-
// middle
10-
for (int i = 1; i < spaces.length; i++) {
11-
stringBuilder.append(s, spaces[i - 1], spaces[i]).append(" ");
3+
int n = spaces.length;
4+
StringBuilder ans = new StringBuilder();
5+
ans.append(s, 0, spaces[0]).append(" "); // 也可以加 0 和 s.length() 两个哨兵
6+
for (int i = 1; i < n; i++) {
7+
ans.append(s, spaces[i - 1], spaces[i]).append(" ");
128
}
13-
// last
14-
stringBuilder.append(s, last, s.length());
15-
return stringBuilder.toString();
9+
ans.append(s, spaces[n - 1], s.length());
10+
return ans.toString();
1611
}
1712
}
1813
/*
@@ -27,4 +22,5 @@ public String addSpaces(String s, int[] spaces) {
2722
请你添加空格,并返回修改后的字符串。
2823
2924
java 字符串是不可变类型,因此不用考虑在原字符串上插入空格导致下标变化问题,直接新开一个 StringBuilder 模拟即可。
25+
StringBuilder#append(CharSequence s, int start, int end) 等价于 StringBuilder#append(s[start:end])
3026
*/

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