969. Pancake Sorting.java

class Solution {
    public List<Integer> pancakeSort(int[] A) {
        List<Integer> res = new ArrayList<>();
        for (int i = A.length, j; i > 0; --i) {
            for (j = 0; A[j] != i; j++)
                ;
            reverse(A, j);
            res.add(j + 1);
            reverse(A, i - 1);
            res.add(i);
        }
        return res;
    }

    public void reverse(int[] A, int k) {
        int i = 0, j = k;
        while (i < j) {
            A[i] ^= A[j];
            A[j] ^= A[i];
            A[i] ^= A[j];
            i++;
            j--;
        }
    }
}