package no329; import java.io.FileNotFoundException; import java.io.IOException; import java.io.InputStream; import java.io.PrintWriter; import java.util.InputMismatchException; import java.util.NoSuchElementException; public class Main { public static final long MOD = 1000000007; public static final long MOD_SQ = MOD * MOD; public static final int WMAX = 1000; static long[] fact = Mod.factorialArray(WMAX, MOD); static long[][] comb = Mod.combinationArray(1000, 1000, MOD); static long[][] pow = new long[WMAX+1][WMAX+1]; public static void main(String[] args) throws FileNotFoundException { long stime = System.nanoTime(); for(int i=1;i<=WMAX;i++) { pow[i][0] = 1; for(int j=1;j<=WMAX;j++) { pow[i][j] = pow[i][j-1] * i % MOD; } } // IO io = new IO(new FileInputStream("329.txt")); IO io = new IO(); int n = io.nextInt(); int m = io.nextInt(); int[] w = new int[n]; for(int i=0;i= w[j]) { int a = w[i]; int b = w[j]; if (a == b) { ans += fact[a]; }else{ if (memo[a][b] != 0) { ans += memo[a][b]; }else{ long sum = 0; for(int k=0;k<=b;k++) { long x = comb[b][k] * pow[k][a]; if ((b - k) % 2 == 0) { sum += x; }else{ sum += (MOD_SQ - x); } if (sum >= MOD_SQ) { sum -= MOD_SQ; } } // System.out.println(i + "," + j + ":" + a + "->" + b + ":" + sum % MOD); ans += memo[a][b] = sum; } } if (ans >= MOD_SQ) { ans -= MOD_SQ; } } } } System.out.println(ans % MOD); // System.out.println((System.nanoTime() - stime) / 1000000 + " ms"); } } class Mod { public static long[] factorialArray(int maxN,long mod) { long[] fact = new long[maxN+1]; fact[0] = 1 % mod; for(int i=1;i<=maxN;i++) { fact[i] = fact[i-1] * i % mod; } return fact; } public static long[][] combinationArray(int maxN,int maxR,long mod) { long[][] c = new long[maxN+1][maxR+1]; for(int i=0;i<=maxN;i++) { c[i][0] = 1; c[i][i] = 1; } for(int i=1;i<=maxN;i++) { for(int j=1;j<=i-1;j++) { c[i][j] = c[i-1][j-1] + c[i-1][j]; if (c[i][j] >= mod) { c[i][j] -= mod; } } } return c; } public static long pow(long a,long n,long mod) { long res = 1; while(n > 0) { if ((n & 1) > 0) { res = (res * a) % mod; } a = (a * a) % mod; n/=2; } return res; } } class IO extends PrintWriter { private final InputStream in; private final byte[] buffer = new byte[1024]; private int ptr = 0; private int buflen = 0; public IO() { this(System.in);} public IO(InputStream source) { super(System.out); this.in = source;} 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 static boolean isNewLine(int c) { return c == '\n' || c == '\r';} public boolean hasNext() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++; return hasNextByte();} public boolean hasNextLine() { while(hasNextByte() && isNewLine(buffer[ptr])) ptr++; return hasNextByte();} 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 char[] nextCharArray(int len) { if (!hasNext()) { throw new NoSuchElementException(); } char[] s = new char[len]; int i = 0; int b = readByte(); while(isPrintableChar(b)) { if (i == len) { throw new InputMismatchException(); } s[i++] = (char) b; b = readByte(); } return s; } public String nextLine() { if (!hasNextLine()) { throw new NoSuchElementException(); } StringBuilder sb = new StringBuilder(); int b = readByte(); while(!isNewLine(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(); } } public int nextInt() { long nl = nextLong(); if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) { throw new NumberFormatException(); } return (int) nl; } public char nextChar() { if (!hasNext()) { throw new NoSuchElementException(); } return (char) readByte(); } public double nextDouble() { return Double.parseDouble(next());} public int[] nextIntArray(int n) { int[] a = new int[n]; for(int i=0;i