java - 什么是 map[(int)x]++; 它有什么作用？

Question

嘿，我参加了 Facebook 黑客竞赛，我得到了这个问题的解决方案。我按 O(K^2) 的顺序解决了这个问题，但是这个人在 O(^K) 中解决了它。请向我解释代码的作用。

    import java.io.File;
    import java.util.Scanner;

     public class FindTheMin {

private long getNextMin(long[] map, long start, long k) {
    while (map[(int)(start)] > 0)
        start++;
    return start;
}

public long findNth(long n, long k, long a, long b, long c, long r) {
    long[] cache = new long[100010];
    long[] map = new long[100010];
    long pre = a;
    for (int i = 0; i < k; i++) {
        long num;
        if (i == 0)
            num = a;
        else
            num = (b * pre + c) % r;
        cache[i] = num;
        if (num <= k + 1)
            map[(int) num]++;
        pre = num;
    }

    pre = getNextMin(map, 0, k);
    cache[(int)k] = pre;
    map[(int)pre]++;
    for (int i = 0; i <= (int)k; i++) {
        long deque = cache[i];
        if (deque > k) {
            long x = getNextMin(map, pre, k);
            cache[i] = x;
            map[(int)x]++;
            pre = x;
        } else {
            if (deque < pre) {
                if(map[(int)deque] == 1) {
                    cache[i] = deque;
                    pre = deque;
                    continue;
                }
            }
            map[(int)deque]--;
            long x = getNextMin(map, pre, k);
            cache[i] = x;
            pre = x;
            map[(int)x]++;
        }
    }

    return cache[(int)((n - 1) % (k + 1))];
}

public static void main(String[] args) {
    try {
        Scanner s = new Scanner(new File("in.txt"));
        int m = s.nextInt();
        FindTheMin f = new FindTheMin();

        for (int i = 1; i <= m; i++) {
            int n, k, a, b, c, r;
            n = s.nextInt();
            k = s.nextInt();
            a = s.nextInt();
            b = s.nextInt();
            c = s.nextInt();
            r = s.nextInt();
            System.out.println("Case #" + i + ": " + f.findNth(n, k, a, b, c, r));
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}

}

学习此类内容的最佳方法是什么。学习java的最好方法？这是问题 https://www.facebook.com/hackercup/problems.php?pid=494433657264959&round=185564241586420

Answer 1

map[(int)x]++ 与以下内容相同:

int index = (int) x;
map[index]++;