Language: Java


import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.math.BigInteger;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.stream.Stream;

public class Main {

    public static void main(String[] args) throws IOException {
        new Main().solve();
    }

    private void solve() throws IOException {
        try {
            //			solveA();
            //			solveB();
            //			solveC();
            solveD();
            //			 solveE();
            //			 solveF();
        } finally {
            if (in != null) {
                in.close();
            }
            if (out != null) {
                out.flush();
                out.close();
            }
        }

    }

    private void solveA() {
        int n = nextInt();

        out.println(n * n);
    }

    private void solveB() {
        int n = nextInt();
        char[] s = next().toCharArray();
        if (s.length < 2 || s.length % 2 != 0) {
            out.println("No");
            return;
        }
        int add = (n / 2);
        for (int i = 0; i < add; i++) {
            if (s[i] != s[i + add]) {
                out.println("No");
                return;
            }
        }

        out.println("Yes");
    }

    private void solveC() {
        int n = nextInt();
        int[][] wk = Stream.generate(() -> new int[]{nextInt(), nextInt()}).limit(n).toArray(int[][]::new);
        double res = 0;
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                res += Math.sqrt(Math.pow(wk[i][0] - wk[j][0], 2) + Math.pow(wk[i][1] - wk[j][1], 2));
            }
        }

        out.println(res / n);
    }

    private void solveCRecursive() {
        int n = nextInt();
        int[][] wk = Stream.generate(() -> new int[]{nextInt(), nextInt()}).limit(n).toArray(int[][]::new);
        double res = permutation(n, 0, wk, new boolean[n], 0, 0);
        out.println(res / totalPerm);
    }

    private int totalPerm = 0;

    private double permutation(int n, int prenum, int[][] wk, boolean[] visited, double total, int vn) {
        if (vn >= n) {
            totalPerm++;
            return total;
        }
        double sum = 0;
        for (int i = 0; i < n; i++) {
            if (!visited[i]) {
                visited[i] = true;
                double wkTotal = total;
                if (vn != 0)
                    wkTotal += Math.sqrt(Math.pow(wk[prenum][0] - wk[i][0], 2) + Math.pow(wk[prenum][1] - wk[i][1], 2));
                sum += permutation(n, i, wk, visited, wkTotal, vn + 1);
                visited[i] = false;
            }
        }
        return sum;
    }

    private void solveD() {
        int x = nextInt();
        int y = nextInt();

        /*
        (x+1,y+2) || (x+2,y+1)
        なので、1回の移動量は+3
        3の倍数でない場合はたどり着けない
         */
        if ((x + y) % 3 != 0) {
            out.println(0);
            return;
        }

        /*
        (x+1,y+2) || (x+2,y+1)
        それぞれn回、m回移動するとして連立方程式を立てる
        X = (+1)*n + (+2)*m = n+2m = n+2m
        Y = (+2)*n + (+1)*m = 2n+m = 2n+m
        X - 2m = n
        Y = 2(X-2m) + m
          = 2X - 4m + m
          = 2X - 3m
        3m = 2X - Y
        m = (2X - Y) / 3
        n = X - 2 * ((2X - Y) / 3)
        もし、 n < 0 || m < 0 なら移動不可
         */
        int m = (2 * x - y) / 3;
        int n = x - 2 * m;
        if (m < 0 || n < 0) {
            out.println(0);
            return;
        }

        /*
        残りは、 n * m回の異動がある
         */
        final long CONST_MOD = (long) (Math.pow(10, 9) + 7;
        long mole = 1;
        for (int i = 1; i <= n + m; i++) {
            mole *= i;
            mole %= CONST_MOD;
        }
        long deno = 1;
        for (int i = 1; i <= n; i++) {
            deno *= i;
            deno %= CONST_MOD;
        }
        for (int i = 1; i <= m; i++) {
            deno *= i;
            deno %= CONST_MOD;
        }
        /*
         * mod 100000007における denoの逆元を求める
         * deno^-1(mod CONST_MOD)
         */
        BigInteger denoModInverse = new BigInteger(Long.toString(deno))
                .modInverse(new BigInteger(Long.toString(CONST_MOD)));

        out.println(new BigInteger(Long.toString(mole)).multiply(denoModInverse)
                .mod(new BigInteger(Long.toString(CONST_MOD))));

    }

    private void solveE() {
        int n = nextInt();

        out.println("");
    }

    private void solveF() {
        int n = nextInt();

        out.println("");
    }

    /*
     * 階乗計算の最大値
     * もっと大きいのが必要ならここを修正
     */
    private final int FACTORIAL_NUM = 111111;
    /*
     * 階乗の事前計算（mod 済）
     */
    private long[] factorial = new long[FACTORIAL_NUM];
    /*
     * 逆数の事前計算（mod 済）
     */
    private long[] reverseFactorial = new long[FACTORIAL_NUM];
    private boolean isInitFactorial = false;

    /**
     * 階乗計算の事前累積和
     * [1, 1, 2, 3, 4, 5, … FACTORIAL_NUM]
     * mod済
     */
    private void initFactorial(long mod) {
        factorial[0] = 1;
        for (int i = 1; i < FACTORIAL_NUM; i++) {
            factorial[i] = (factorial[i - 1] * i) % mod;
        }
    }

    /**
     * 逆数の事前計算
     * もっと速い方法があったので修正
     */
    private void initReverseFactorial(long mod) {

        reverseFactorial[0] = 1;
        for (int i = 0; i < FACTORIAL_NUM; i++) {
            reverseFactorial[i] = modInverse(factorial[i], mod);
        }
    }

    /**
     * フェルマーの小定理を用いて逆元を求める。
     * ある数xのmod p（pは素数）の逆数x'はx' = x^(p-2)
     * 繰り返し二乗法を用いて計算する。
     * http://satanic0258.hatenablog.com/entry/2016/04/29/004730
     * {@link BigInteger#modInverse(BigInteger)}とどちらが速いか？
     *
     * @param x
     * @return
     */
    private long modInverse(long x, long mod) {
        long res = 1L;
        long k = mod - 2L;
        long y = x;
        while (k != 0) {
            if (k % 2 != 0) {
                res = (res * y) % mod;
            }
            y = (y * y) % mod;
            k /= 2;
        }
        return res;
    }

    private void initFactorialCalc(long mod) {
        if (isInitFactorial) {
            //初期化済みならreturn
            return;
        }
        //階乗の事前計算
        initFactorial(mod);
        //逆数の計算もしておく
        initReverseFactorial(mod);
        isInitFactorial = true;
    }

    /**
     * 組み合わせ
     * nCk -> n! / k!・(n-k)!
     *
     * @param n
     * @param k
     * @param mod
     * @return
     */
    private long combination(int n, int k, long mod) {
        initFactorialCalc(mod);
        if (k < 0 || n < k) {
            return 0;
        }

        //分子の計算
        long calResN = factorial[n];

        //分母の計算
        long calResNK = reverseFactorial[n - k];
        long calcResK = reverseFactorial[k];
        long denominator = (calResNK * calcResK) % mod;

        return (calResN * denominator) % mod;

    }

    /**
     * 順列
     * nPk -> n! / (n-k)!
     *
     * @param n
     * @param k
     * @return
     */
    private long permutation(int n, int k, long mod) {
        initFactorialCalc(mod);
        if (k < 0 || n < k) {
            return 0;
        }
        long calResN = factorial[n];
        long calResNK = reverseFactorial[n - k];
        return (calResN * calResNK) % mod;
    }

    /**
     * 多項係数
     * 文字aをp個,bをq個,cをr個, dをs個 あわせてn個を1列に並べるときの並べ方
     * n! / p!・q!・r!・s!
     *
     * @param n
     * @param strNum
     * @param mod
     * @return
     */
    private long multinominalCoefficient(int n, List<Integer> strNum, int mod) {
        initFactorialCalc(mod);

        long calResN = factorial[n];
        long calResDenomi = 1;
        for (Integer num : strNum) {
            calResDenomi *= reverseFactorial[num];
        }
        return (calResN * calResDenomi) % mod;
    }

    /**
     * 重複組合せ nHr （同次積）
     * nHr = (n+r-1)Cr
     * 異なるn個のものから重複を許してr個取る組合せの総数
     * 例：
     * リンゴ，ミカン，牛肉の3種類の果物があります．これらの中から6個の食材を買って帰ります．
     * このとき，何通りの買い方がありますか？ただし，含まれない食材があってもよいものとします
     *
     * @param n
     * @param r
     * @param mod
     * @return
     */
    private long homogeneousProduct(int n, int r, long mod) {
        if (n == 0 && r == 0) {
            return 1;
        }
        return combination(n + r - 1, r, mod);
    }

    private final PrintWriter out = new PrintWriter(System.out);
    private final InputStream in = System.in;
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;

    private boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        } else {
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    }

    private int readByte() {
        if (hasNextByte())
            return buffer[ptr++];
        else
            return -1;
    }

    private static boolean isPrintableChar(int c) {
        return 33 <= c && c <= 126;
    }

    private void skipUnprintable() {
        while (hasNextByte() && !isPrintableChar(buffer[ptr]))
            ptr++;
    }

    public boolean hasNext() {
        skipUnprintable();
        return hasNextByte();
    }

    public int nextInt() {
        return Integer.parseInt(next());
    }

    public String next() {
        if (!hasNext())
            throw new NoSuchElementException();
        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while (isPrintableChar(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    }

    public long nextLong() {
        if (!hasNext())
            throw new NoSuchElementException();
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while (true) {
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            } else if (b == -1 || !isPrintableChar(b)) {
                return minus ? -n : n;
            } else {
                throw new NumberFormatException();
            }
            b = readByte();
        }
    }
}

Compiler output:
Main.java:139: error: ')' expected
        final long CONST_MOD = (long) (Math.pow(10, 9) + 7;
                                                          ^
1 error