gistfile1.groovy

int[] a = [1, 2, 3, 4, 5, 6, 7, 8, 9]
int[] b = [1, 2, 3, 4, 9, 8, 7, 6, 5]
int[] e = [9, 1, 8, 2, 7, 3, 6, 4, 5]
int[] f = [9, 8, 7, 6, 5, 4, 3, 2, 1]

int[] c = [1, 2, 3, 4, 5, 6, 7, 8, 10]
int[] d = [1, 2, 3, 4, 5, 6, 7, 8, 8]
int[] g = [1, 8, 3, 4, 5, 6, 7, 8, 8]


def check(int[] a) {
    println a
    int N = a.length
    int i = 0
    while (i < N) {
        int c = a[i]
        print i
        println c
        // out of range
        if (c < 1 || c > N) {
            return false
        }
        // duplicate
        if (c <= i) {
            return false
        }
        // swap
        if (c != i + 1) {
            int t = a[c - 1]
            if (t == c) {
                return false;
            }
            a[c - 1] = c
            a[i] = t
        } else {
            i++
        }
    }
    return true;
}

assert check(a)
assert check(b)
assert check(e)

assert !check(c)
assert !check(d)
assert !check(g)