class Solution {public:    int removeElement(int A[], int n, int elem) {        if (A == NULL || n < 1) return 0;        int rpos = 0, wpos = 0;        int removed = 0;        while (rpos < n) {            if (A[rpos] == elem) {                rpos++;                removed++;            } else {                A[wpos++] = A[rpos++];            }        }        return n - removed;    }};