【 NO.1 执行操作后的变量值】
解题思路
签到题。
代码展现
class Solution {
public int finalValueAfterOperations(String[] operations) {
int v = 0; for (String op : operations) { if (op.contains("++")) { v++; } else { v--; } } return v;}
}
【 NO.2 数组漂亮值求和】
解题思路
由前缀最大值和后缀最小值即可失去两头元素的漂亮值，所以预处理出前缀最大值和后缀最小值数组即可。
代码展现
class Solution {
public int sumOfBeauties(int[] nums) {
int[] preMax = new int[nums.length]; preMax[0] = nums[0]; for (int i = 1; i < nums.length; i++) { preMax[i] = Math.max(preMax[i - 1], nums[i]); } int[] sufMin = new int[nums.length]; sufMin[nums.length - 1] = nums[nums.length - 1]; for (int i = nums.length - 2; i >= 0; i--) { sufMin[i] = Math.min(sufMin[i + 1], nums[i]); } int res = 0; for (int i = 1; i < nums.length - 1; ++i) { if (preMax[i - 1] < nums[i] && nums[i] < sufMin[i + 1]) { res += 2; } else if (nums[i - 1] < nums[i] && nums[i] < nums[i + 1]) { res += 1; } } return res;}
}
【 NO.3 检测正方形】
解题思路
应用 Map 贮存所有的顶点，而后在 count 查问时枚举对角线。
代码展现
class DetectSquares {
Map<Integer, Integer> count;
public DetectSquares() {
count = new HashMap<>();}
public void add(int[] point) {
int c = comp(point[0], point[1]); count.put(c, count.getOrDefault(c, 0) + 1);}
public int count(int[] point) {
int res = 0; for (var kv : count.entrySet()) { int x = X(kv.getKey()); int y = Y(kv.getKey()); if (Math.abs(x - point[0]) == Math.abs(y - point[1]) && x != point[0]) { res += kv.getValue() * count.getOrDefault(comp(x, point[1]), 0) * count.getOrDefault(comp(point[0], y), 0); } } return res;}
private int comp(int x, int y) {
return x * 10000 + y;}
private int X(int c) {
return c / 10000;}
private int Y(int c) {
return c % 10000;}
}
【 NO.4 反复 K 次的最长子序列】
解题思路
留神 2 <= n < k * 8，而如果一个子序列想要反复呈现 k 次，那么这个子序列中的每个字符都至多要呈现 k 次，所以说答案的长度肯定小于等于 7。
咱们首先找进去所有呈现次数不小于 k 次的字符，而后枚举这些字符的排列组合，顺次判断每一个排列组合是否呈现了 k 次。
代码展现
class Solution {
public String longestSubsequenceRepeatedK(String s, int k) {
Map<Character, Integer> count = new HashMap<>(); for (char c : s.toCharArray()) { count.put(c, count.getOrDefault(c, 0) + 1); } StringBuilder s2 = new StringBuilder(); for (char c : s.toCharArray()) { if (count.get(c) >= k) { s2.append(c); } } count.clear(); for (char c : s2.toString().toCharArray()) { count.put(c, count.getOrDefault(c, 0) + 1); } return solve(new StringBuilder(), count, s2.toString().toCharArray(), k);}
private String solve(StringBuilder cur, Map<Character, Integer> count, char[] s, int k) {
String res = ""; var keys = new HashSet<Character>(count.keySet()); for (var c : keys) { cur.append(c); if (comp(cur.toString(), res)) { int cnt = 0, idx = 0; for (char cc : s) { if (cc == cur.charAt(idx) && ++idx == cur.length()) { idx = 0; if (++cnt == k) { res = cur.toString(); break; } } } } int bak = count.get(c); if (bak - k < k) { count.remove(c); } else { count.put(c, bak - k); } String r = solve(cur, count, s, k); if (comp(r, res)) { res = r; } cur.deleteCharAt(cur.length() - 1); count.put(c, bak); } return res;}
private boolean comp(String a, String b) {
return a.length() > b.length() || (a.length() == b.length() && a.compareTo(b) > 0);}
}