方法

使用左右两个标记。

    public int removeElement(int[] A, int elem) {
        if (A == null || A.length == 0) {
            return 0;
        }
        int len = A.length;
        int left = 0;
        int right = len - 1;
        while (left < right) {
            while (left < right && A[left] != elem) {
                left++;
            }
            while(left < right && A[right] == elem) {
                right--;
            }
            if (left < right) {
                int temp = A[left];
                A[left] = A[right];
                A[right] = temp;
            }
        }
        if (A[left] != elem) {
        	left = left + 1;
        }
        return left;
    }