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算法时间复杂度和真实时间测算

article 2024/11/7 8:16:56

一维度循环 1后面9个0

public class Main {
    public static void main(String[] args) {
        long l1 = System.currentTimeMillis();

        long x = 0;
        long N = (long) 1e9;
        for (long i = 0; i < N; i++) {
            if (i % 2 == 0) {
                x += i;
            } else {
                x -= i;
            }
        }
        long l2 = System.currentTimeMillis();
        System.out.println(l2 - l1);
    }
}

二维循环

public class Main {
    public static void main(String[] args) {
        long l1 = System.currentTimeMillis();

        long x = 0;
        for (long i = 0; i < 10000; i++) {
            for (long j = 0; j < 100000; j++) {
                x = x+i+j;
            }
        }
        long l2 = System.currentTimeMillis();
        System.out.println(l2 - l1);
    }
}

三维循环

public class Main {
    public static void main(String[] args) {
        long l1 = System.currentTimeMillis();

        long x = 0;
        for (long i = 0; i < 1000; i++) {
            for (long j = 0; j < 1000; j++) {
                for (long k = 0; k < 1000; k++) {
                    x = x + i - j + k;
                }
            }
        }
        long l2 = System.currentTimeMillis();
        System.out.println(l2 - l1);
    }
}

快速排序

public class Main {
    public static void main(String[] args) {
        int N = 39620077; // 数组长度
        int[] randomArray = new int[N];

        Random random = new Random();

        // 填充数组
        for (int i = 0; i < N; i++) {
            randomArray[i] = random.nextInt(); // 生成随机整数
        }

        long l1 = System.currentTimeMillis();
        Arrays.sort(randomArray);
        long l2 = System.currentTimeMillis();
        System.out.println(l2 - l1);

    }
}