55 lines
1.4 KiB
Java
55 lines
1.4 KiB
Java
import java.util.Arrays;
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// https://www.hackerearth.com/notes/mos-algorithm/
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// Solution of http://www.spoj.com/problems/DQUERY/en/
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public class MosAlgorithm {
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public static class Query {
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int index;
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int a;
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int b;
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public Query(int a, int b) {
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this.a = a;
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this.b = b;
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}
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}
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static int add(int[] a, int[] cnt, int i) {
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return ++cnt[a[i]] == 1 ? 1 : 0;
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}
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static int remove(int[] a, int[] cnt, int i) {
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return --cnt[a[i]] == 0 ? -1 : 0;
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}
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public static int[] processQueries(int[] a, Query[] queries) {
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for (int i = 0; i < queries.length; i++) queries[i].index = i;
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int sqrtn = (int) Math.sqrt(a.length);
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Arrays.sort(queries, (q1, q2) -> {
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int cmp = Integer.compare(q1.a / sqrtn, q2.a / sqrtn);
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return cmp != 0 ? cmp : Integer.compare(q1.b, q2.b);
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});
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int[] cnt = new int[1000_002];
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int[] res = new int[queries.length];
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int L = 1;
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int R = 0;
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int cur = 0;
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for (Query query : queries) {
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while (L < query.a) cur += remove(a, cnt, L++);
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while (L > query.a) cur += add(a, cnt, --L);
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while (R < query.b) cur += add(a, cnt, ++R);
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while (R > query.b) cur += remove(a, cnt, R--);
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res[query.index] = cur;
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}
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return res;
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}
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public static void main(String[] args) {
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int[] a = {1, 3, 3, 4};
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Query[] queries = {new Query(0, 3), new Query(1, 3), new Query(2, 3), new Query(3, 3)};
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int[] res = processQueries(a, queries);
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System.out.println(Arrays.toString(res));
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}
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}
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