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package class_2022_09_2_week;
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import java.util.HashMap;
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// 来自微软
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// 给定一个字符串s，其中都是英文小写字母
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// 如果s中的子串含有的每种字符都是偶数个
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// 那么这样的子串就是达标子串，子串要求是连续串
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// 返回s中达标子串的最大长度
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// 1 <= s的长度 <= 10^5
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// 字符种类都是英文小写
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public class Code03_EvenTimesMaxSubstring {
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// 为了测试
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// 暴力方法
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public static int maxLen1(String s) {
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int n = s.length();
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int ans = 0;
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for (int i = 0; i < n; i++) {
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for (int j = n - 1; j >= i; j--) {
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if (ok(s, i, j)) {
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ans = Math.max(ans, j - i + 1);
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break;
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}
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}
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}
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return ans;
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}
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// 为了测试
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// 暴力方法
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public static boolean ok(String s, int l, int r) {
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if (((r - l + 1) & 1) == 1) {
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return false;
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}
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int[] cnts = new int[26];
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for (int i = l; i <= r; i++) {
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cnts[s.charAt(i) - 'a']++;
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}
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for (int cnt : cnts) {
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if ((cnt & 1) == 1) {
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return false;
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}
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}
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return true;
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}
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public static int maxLen2(String s) {
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HashMap<Integer, Integer> map = new HashMap<>();
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map.put(0, -1);
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int status = 0;
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int ans = 0;
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int n = s.length();
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for (int i = 0; i < n; i++) {
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status ^= 1 << (s.charAt(i) - 'a');
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if (map.containsKey(status)) {
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ans = Math.max(ans, i - map.get(status));
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} else {
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map.put(status, i);
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}
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}
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return ans;
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}
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// 为了测试
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public static String randomString(int n, int v) {
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char[] s = new char[n];
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for (int i = 0; i < n; i++) {
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s[i] = (char) ((int) (Math.random() * v) + 'a');
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}
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return String.valueOf(s);
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}
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// 为了测试
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public static void main(String[] args) {
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int n = 50;
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int v = 6;
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int testTimes = 2000;
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System.out.println("测试开始");
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for (int i = 0; i < testTimes; i++) {
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String s = randomString(n, v);
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int ans1 = maxLen1(s);
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int ans2 = maxLen2(s);
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if (ans1 != ans2) {
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System.out.println(s);
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System.out.println(ans1);
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System.out.println(ans2);
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break;
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}
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}
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System.out.println("测试结束");
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}
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}
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