27.移除元素

    public int removeElement(int[] nums, int val) {
        int n =  nums.length;
        if (n == 0) {
            return 0;
        }
        int fast = 0;
        int slow = 0;
        while (fast < n) {
            if (nums[fast] != val) {
                nums[slow] = nums[fast];
                slow ++;
            }
            fast ++;
        }
        return slow;
    }