Problem:
Score : 1700 points

Problem Statement

Snuke has an integer sequence A whose length is N.
He likes permutations of (1, 2, ..., N), P, that satisfy the following condition:

P_i \leq A_i for all i ( 1 \leq i \leq N ).

Snuke is interested in the inversion numbers of such permutations.
Find the sum of the inversion numbers over all permutations that satisfy the condition.
Since this can be extremely large, compute the sum modulo 10^9+7.

Notes

The inversion number of a sequence Z whose length N is the number of pairs of integers i and j ( 1 \leq i < j \leq N ) such that Z_i > Z_j.

Constraints

1 \leq N \leq 2 \times 10^5

1 \leq A_i \leq N ( 1 \leq i \leq N )

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
A_1 A_2 ... A_N

Output

Print the sum of the inversion numbers over all permutations that satisfy the condition.

Sample Input 1

3
2 3 3

Sample Output 1

4

There are four permutations that satisfy the condition: (1,2,3), (1,3,2), (2,1,3) and (2,3,1).
The inversion numbers of these permutations are 0, 1, 1 and 2, respectively, for a total of 4.

Sample Input 2

6
4 2 5 1 6 3

Sample Output 2

7

Only one permutation (4,2,5,1,6,3) satisfies the condition.
The inversion number of this permutation is 7, so the answer is 7.

Sample Input 3

5
4 4 4 4 4

Sample Output 3

0

No permutation satisfies the condition.

Sample Input 4

30
22 30 15 20 10 29 11 29 28 11 26 10 18 28 22 5 29 16 24 24 27 10 21 30 29 19 28 27 18 23

Sample Output 4

848414012

Solution in Java7 (OpenJDK 1.7.0) (judge verdict: Accepted)

import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Arrays;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;
import java.io.BufferedReader;
import java.util.ArrayDeque;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskE solver = new TaskE();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskE {
        static final long MODULO = (long) 1e9 + 7;
        ArrayDeque<int[]> available = new ArrayDeque<>();
        int totalAllocated = 0;
        int n;
        int[] a;
        int[] w;

        int[] newMatrix() {
            ++totalAllocated;
            if (available.isEmpty()) {
                return new int[9];
            } else {
                int[] res = available.pop();
                Arrays.fill(res, 0);
                return res;
            }
        }

        void freeMatrix(int[] a) {
            --totalAllocated;
            available.push(a);
        }

        int[] mul(int[] a, int[] b) {
            int[] c = newMatrix();
            for (int i = 0; i < 3; ++i) {
                for (int j = 0; j < 3; ++j) {
                    long s = 0;
                    for (int k = 0; k < 3; ++k) s += a[(i) * 3 + k] * (long) b[(k) * 3 + j];
                    c[(i) * 3 + j] = (int) (s % MODULO);
                }
            }
            return c;
        }

        int[] add(int[] a, int[] b) {
            int[] c = newMatrix();
            for (int i = 0; i < 3; ++i) {
                for (int j = 0; j < 3; ++j) {
                    long s = a[(i) * 3 + j] + b[(i) * 3 + j];
                    c[(i) * 3 + j] = (int) (s % MODULO);
                }
            }
            return c;
        }

        public void solve(int testNumber, InputReader in, PrintWriter out) {
            n = in.nextInt();
            a = new int[n];
            for (int i = 0; i < n; ++i) a[i] = in.nextInt();
            for (int i = 0, j = n - 1; i < j; ++i, --j) {
                int t = a[i];
                a[i] = a[j];
                a[j] = t;
            }
            int[] positions = new int[n];
            for (int i = 0; i < n; ++i) positions[i] = i;
            w = getW(a.clone());
            for (int x : w)
                if (x == 0) {
                    out.println(0);
                    return;
                }

            Description desc = doit(0, n - 1, positions);
            out.println(desc.inside[(2) * 3 + 0]);
            desc.freeAll();
            if (totalAllocated != 0) throw new RuntimeException("" + totalAllocated);
        }

        private int[] getW(int[] a) {
            Arrays.sort(a);
            int sofar = 0;
            int pos = a.length - 1;
            int[] w = new int[n];
            for (int i = n - 1; i >= 0; --i) {
                while (pos >= 0 && a[pos] == i + 1) {
                    ++sofar;
                    --pos;
                }
                w[i] = Math.max(0, sofar);
                --sofar;
            }
            return w;
        }

        private Description doit(int min, int max, int[] positions) {
            Description res = new Description();
            if (min == max) {
                res.p00then01 = new int[positions.length][];
                res.p00then10 = new int[positions.length][];
                res.p01then11 = new int[positions.length][];
                res.p10then11 = new int[positions.length][];
                int k = min;
                for (int x : positions) if (a[x] != k + 1) throw new RuntimeException();
                res.p00 = newMatrix();
                res.p00[(0) * 3 + 0] = w[k];
                res.p01 = newMatrix();
                res.p01[(0) * 3 + 0] = w[k] - 1;
                res.p01[(1) * 3 + 0] = 1;
                res.p01[(1) * 3 + 1] = w[k];
                res.p10 = newMatrix();
                res.p10[(0) * 3 + 0] = w[k] - 1;
                res.p11 = newMatrix();
                res.p11[(0) * 3 + 0] = Math.max(0, w[k] - 2);
                res.p11[(1) * 3 + 0] = 1;
                res.p11[(1) * 3 + 1] = w[k] - 1;
                res.p11[(2) * 3 + 1] = 1;
                res.p11[(2) * 3 + 2] = w[k];
                for (int i = 0; i < positions.length; ++i) {
                    res.p01then11[i] = copy(res.p11);
                    res.p10then11[i] = copy(res.p11);
                    res.p00then10[i] = copy(res.p10);
                    res.p00then01[i] = copy(res.p01);
                }
                int[] sum = newMatrix();
                res.inside = newMatrix();
                for (int x : positions) {
                    int[] tmp1 = res.inside;
                    res.inside = add(res.inside, sum);
                    freeMatrix(tmp1);
                    tmp1 = sum;
                    sum = add(sum, res.p11);
                    freeMatrix(tmp1);
                }
                freeMatrix(sum);
            } else {
                int mid = (min + max) / 2;
                int numBottom = 0;
                int numTop = 0;
                for (int x : positions)
                    if (a[x] <= mid + 1) {
                        ++numBottom;
                    } else {
                        ++numTop;
                    }
                int[] bottomPositions = new int[numBottom];
                int[] topPositions = new int[numTop];
                numBottom = 0;
                numTop = 0;
                for (int x : positions)
                    if (a[x] <= mid + 1) {
                        bottomPositions[numBottom++] = x;
                    } else {
                        topPositions[numTop++] = x;
                    }
                Description bottom;
                Description top;
                if (numBottom < numTop) {
                    bottom = doit(min, mid, bottomPositions);
                    top = doit(mid + 1, max, topPositions);
                } else {
                    top = doit(mid + 1, max, topPositions);
                    bottom = doit(min, mid, bottomPositions);
                }
                res.p00then01 = new int[positions.length][];
                res.p00then10 = new int[positions.length][];
                res.p01then11 = new int[positions.length][];
                res.p10then11 = new int[positions.length][];
                int[] tmp1 = mul(bottom.inside, top.p00);
                int[] tmp2 = mul(bottom.p11, top.inside);
                res.inside = add(tmp1, tmp2);
                freeMatrix(tmp1);
                freeMatrix(tmp2);
                res.p00 = mul(bottom.p00, top.p00);
                res.p11 = mul(bottom.p11, top.p11);
                res.p01 = mul(bottom.p01, top.p01);
                res.p10 = mul(bottom.p10, top.p10);
                int topPtr = 0;
                int bottomPtr = 0;
                int[] topSum = newMatrix();
                int[] bottomSum = newMatrix();
                int ptr = 0;
                for (int x : positions)
                    if (a[x] <= mid + 1) {
                        res.p00then01[ptr] = mul(bottom.p00then01[bottomPtr], top.p00);
                        res.p00then10[ptr] = mul(bottom.p00then10[bottomPtr], top.p00);
                        res.p10then11[ptr] = mul(bottom.p10then11[bottomPtr], top.p10);
                        res.p01then11[ptr] = mul(bottom.p01then11[bottomPtr], top.p01);
                        tmp1 = mul(bottom.p10then11[bottomPtr], topSum);
                        tmp2 = res.inside;
                        res.inside = add(res.inside, tmp1);
                        freeMatrix(tmp1);
                        freeMatrix(tmp2);
                        tmp2 = bottomSum;
                        bottomSum = add(bottomSum, bottom.p01then11[bottomPtr]);
                        freeMatrix(tmp2);
                        ++bottomPtr;
                        ++ptr;
                    } else {
                        res.p00then01[ptr] = mul(bottom.p01, top.p00then01[topPtr]);
                        res.p00then10[ptr] = mul(bottom.p10, top.p00then10[topPtr]);
                        res.p10then11[ptr] = mul(bottom.p11, top.p10then11[topPtr]);
                        res.p01then11[ptr] = mul(bottom.p11, top.p01then11[topPtr]);
                        tmp1 = mul(bottomSum, top.p00then01[topPtr]);
                        tmp2 = res.inside;
                        res.inside = add(res.inside, tmp1);
                        freeMatrix(tmp1);
                        freeMatrix(tmp2);
                        tmp2 = topSum;
                        topSum = add(topSum, top.p00then10[topPtr]);
                        freeMatrix(tmp2);
                        ++topPtr;
                        ++ptr;
                    }
                freeMatrix(bottomSum);
                freeMatrix(topSum);
                bottom.freeAll();
                top.freeAll();
            }
            return res;
        }

        private int[] copy(int[] a) {
            int[] b = newMatrix();
            System.arraycopy(a, 0, b, 0, 9);
            return b;
        }

        class Description {
            int[] inside;
            int[] p00;
            int[] p11;
            int[] p01;
            int[] p10;
            public int[][] p10then11;
            public int[][] p01then11;
            public int[][] p00then01;
            public int[][] p00then10;

            public void freeAll() {
                freeMatrix(inside);
                freeMatrix(p00);
                freeMatrix(p01);
                freeMatrix(p11);
                freeMatrix(p10);
                for (int[] x : p10then11) freeMatrix(x);
                for (int[] x : p01then11) freeMatrix(x);
                for (int[] x : p00then01) freeMatrix(x);
                for (int[] x : p00then10) freeMatrix(x);
            }

        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

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

    }
}