projectEuler 17

将1……n的数表示成英文，求表示成这些英文的字母的和

If the numbers 1 to 5 are written out in words: one, two, three, four, five, then there are 3 + 3 + 5 + 4 + 4 = 19 letters used in total.

If all the numbers from 1 to 1000 (one thousand) inclusive were written out in words, how many letters would be used?

NOTE: Do not count spaces or hyphens. For example, 342 (three hundred and forty-two) contains 23 letters and 115 (one hundred and fifteen) contains 20 letters. The use of "and" when writing out numbers is in compliance with British usage.

思想：

不是很喜欢这题，就是找规律1-19直接替换，然后20,30,40,50,60,70,80,90均有一个英文字符

当数字超过100且不是整数时，需要加上hundred和and10个字母

当数字超过100是整数时，值家hundred7个字母

当数字是1000时，直接的one thousand11个字母

如果有耐心，可以好好的统计规律，求和的时候都不需要迭代，可以一次计算出这个值，我没有那么多耐心，还是老老实实的循环

private static int[] num_letters = { 3, 3, 5, 4, 4, 3, 5, 5, 4, 3, 6, 6, 8,
            8, 7, 7, 9, 8, 8, 6, 6, 5, 5, 5, 7, 6, 6 };

    private static int numLetters(int N) {
        int result = 0, hun = N / 100 % 10, ten = N / 10 % 10, sin = N % 10;
        if (hun > 0) {
            result += num_letters[hun - 1] + 7; // 等于个位数hundred
            if (ten > 0 || sin > 0)
                result += 3;// 如果不是整百需加上'and'
        }
        if (ten == 1) {
            result += num_letters[9 + sin];
        } else {
            if (ten > 1)
                result += num_letters[17 + ten];
            if (sin > 0)
                result += num_letters[sin - 1];
        }

        return result;
    }

    private static int sumLetters(int N) {
        int result = 0;
        if (N == 1000) {
            result += 11;
            N--;
        }
        for (int i = 1; i <= N; i++) {
            result += numLetters(i);
        }

        return result;
    }