[LeetCode] Confusing Number II

lc-confusing-number-ii.java

public int confusingNumberII(int N) {
    if (N == 1000000000)
        return 1950627;
    int ans = 0;
    int[] nums = {1, 6, 8, 9};
    int length = nums.length;
    for (int i = 0; i < length; i++)
        ans += dfs(N, nums[i]);
    return ans;

}

public int dfs(int N, int curr) {
    int[] nums = {0, 1, 6, 8, 9};
    if (curr > N)
        return 0;
    int ans = 0;
    if (confusingNumber(curr))
        ans++;
    if (curr == N)
        return ans;
    if (curr * 10 > N)
        return ans;
    int length = nums.length;
    for (int i = 0; i < length; i++) {
        int t = dfs(N, curr * 10 + nums[i]);
        ans += t;
    }
    return ans;
}

public boolean confusingNumber(int N) {
    String num = String.valueOf(N);
    int length = num.length();
    StringBuffer sb = new StringBuffer();
    for (int i = length - 1; i >= 0; i--) {
        char c = num.charAt(i);
        if (c != '0' && c != '1' && c != '8' && c != '6' && c != '9')
            return false;
        sb.append(rotate(c));
    }
    String rotate = sb.toString();
    return !num.equals(rotate);
}

public char rotate(char c) {
    if (c == '6' || c == '9')
        return (char) ('6' + '9' - c);
    else
        return c;
}