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package class028;
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import java.util.HashMap;
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import java.util.HashSet;
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public class Code03_LongestNoRepeatSubstring {
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/*
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* 给定一个只由小写字母（a~z）组成的字符串str， 返回其中最长无重复字符的子串长度
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*
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*/
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public static int maxNoRepeatSubstringLen1(char[] str) {
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int len = 0;
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for (int L = 0; L < str.length; L++) {
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for (int R = L; R < str.length; R++) {
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HashSet<Character> set = new HashSet<>();
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boolean noRepeat = true;
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for (int i = L; i <= R; i++) {
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if (set.contains(str[i])) {
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noRepeat = false;
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break;
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}
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set.add(str[i]);
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}
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if (noRepeat) {
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int cur = R - L + 1;
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len = Math.max(len, cur);
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}
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}
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}
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return len;
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}
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public static int maxNoRepeatSubstringLen2(char[] str) {
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if (str == null || str.length == 0) {
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return 0;
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}
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int N = str.length;
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int[] dp = new int[N];
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HashMap<Character, Integer> lastMap = new HashMap<>();
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dp[0] = 1;
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lastMap.put(str[0], 0);
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int max = 1;
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for (int i = 1; i < N; i++) {
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int lastIndex = lastMap.containsKey(str[i]) ? lastMap.get(str[i]) : -1;
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int preNo = i - 1 - dp[i - 1];
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int no = Math.max(lastIndex, preNo);
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int curAns = i - no;
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dp[i] = curAns;
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lastMap.put(str[i], i);
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max = Math.max(max, dp[i]);
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}
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return max;
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}
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// for test
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public static String getRandomString(int possibilities, int maxSize) {
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char[] ans = new char[(int) (Math.random() * maxSize) + 1];
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for (int i = 0; i < ans.length; i++) {
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ans[i] = (char) ((int) (Math.random() * possibilities) + 'a');
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}
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return String.valueOf(ans);
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}
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public static void main(String[] args) {
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int possibilities = 26;
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int strMaxSize = 100;
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int testTimes = 10000;
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System.out.println("test begin, test time : " + testTimes);
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for (int i = 0; i < testTimes; i++) {
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String str = getRandomString(possibilities, strMaxSize);
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int ans1 = maxNoRepeatSubstringLen1(str.toCharArray());
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int ans2 = maxNoRepeatSubstringLen2(str.toCharArray());
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if (ans1 != ans2) {
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System.out.println("Oops!");
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}
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}
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System.out.println("test finish");
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}
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}
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