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class Solution {
    public int numDecodings(String s) {
        if (s == null || s.length() == 0 || s.startsWith("0")) return 0;

        if (s.length() == 1) return 1;

        // define dp state
        int dp[] = new int[s.length() + 1];

        // init
        if (s.charAt(0) != '0') dp[0] = 1;
        if (s.charAt(1) != '0') dp[1] = 1;

        for (int i = 2; i < s.length() + 1; i++) {
            int t1 = Integer.parseInt(s.substring(i - 1, i));
            if (1 <= t1 && t1 <= 9) dp[i] += dp[i - 1];

            int t2 = Integer.parseInt(s.substring(i - 2, i));
            if (10 <= t2 && t2 <= 26) dp[i] += dp[i - 2];
        }
        return dp[s.length()];
    }
}

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public class KahanSummation {
    private static float kahanSum(float... fa) {
        float sum = 0.0f;
        float c = 0.0f;
        for (float f : fa) {
            float y = f - c;
            float t = sum + y;
            c = (t - sum) - y;
            sum = t;
        }
        return sum;
    }

    private static float epsilon() {
        float eps = 1.0f;
        while (1.0f + eps != 1.0f) eps /= 2.0f;
        return eps;
    }

    public static void main(String[] args) {
        float a = 1.0f;
        float b = epsilon();
        float c = -b;
        System.out.println("Epsilon      = " + b);
        System.out.println("(a + b) + c  = " + ((a + b) + c));
        System.out.println("Kahan sum    = " + kahanSum(a, b, c));
    }
}