PU Longest Palindromic Subsequence

int longestPalindromeSubseq(char* s) {
    int len = strlen(s);
    if (len == 1) return 1;
    int *bottom = malloc(len * sizeof(int));
    int *top = malloc(len * sizeof(int));
    int i, j;
    for (i = 0; i < len; i++) bottom[i] = 1;
    for (i = 1; i < len; i++) {
        if (s[i] == s[i - 1]) top[i] = 2;
        else top[i] = 1;
    }
    for (i = 2; i < len; i++) {
        int *higher = bottom;
        for (j = len - 1; j >= i; j--) {
            if (s[j] == s[j - i]) higher[j] = 2 + bottom[j - 1];
            else higher[j] = top[j - 1] > top[j] ? top[j - 1] : top[j];
        }
        bottom = top;
        top = higher;
    }
    len = top[len - 1];
    free(bottom);
    free(top);
    return len;
}