Problem:
Score : 600 points

Problem Statement

Snuke has an integer sequence, a, of length N. The i-th element of a (1-indexed) is a_{i}.

He can perform the following operation any number of times:

Operation: Choose integers x and y between 1 and N (inclusive), and add a_x to a_y.

He would like to perform this operation between 0 and 2N times (inclusive) so that a satisfies the condition below. Show one such sequence of operations.
It can be proved that such a sequence of operations always exists under the constraints in this problem.

Condition: a_1 \leq a_2 \leq ... \leq a_{N}

Constraints

2 \leq N \leq 50

-10^{6} \leq a_i \leq 10^{6}

All input values are integers.

Input

Input is given from Standard Input in the following format:

N
a_1 a_2 ... a_{N}

Output

Let m be the number of operations in your solution. In the first line, print m.
In the i-th of the subsequent m lines, print the numbers x and y chosen in the i-th operation, with a space in between.
The output will be considered correct if m is between 0 and 2N (inclusive) and a satisfies the condition after the m operations.

Sample Input 1

3
-2 5 -1

Sample Output 1

2
2 3
3 3

After the first operation, a = (-2,5,4).

After the second operation, a = (-2,5,8), and the condition is now satisfied.

Sample Input 2

2
-1 -3

Sample Output 2

1
2 1

After the first operation, a = (-4,-3) and the condition is now satisfied.

Sample Input 3

5
0 0 0 0 0

Sample Output 3

0

The condition is satisfied already in the beginning.

Solution in Rust (1.15.1) (judge verdict: Accepted)

use std::io::*;
use std::str::FromStr;

#[allow(dead_code)]
fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parse token")
}

fn main() {
    let n: usize = read();
    let mut seq: Vec<i64> = vec![0; n];
    for i in 0..n {
        seq[i] = read();
    }
    let mut max_value = (seq[0], 0);
    let mut min_value = (seq[0], 0);
    for i in 0..n {
        max_value = std::cmp::max(max_value, (seq[i], i));
        min_value = std::cmp::min(min_value, (seq[i], i));
    }
    let mut pos = 0;
    let mut dir = 1;
    let mut src = max_value.1;
    if min_value.0.abs() >= max_value.0.abs() {
        pos = n as i64 - 1;
        dir = -1;
        src = min_value.1;
    }
    println!("{}", 2 * n - 1);
    for i in 0..n {
        // seq[i] += seq[src];
        println!("{} {}", src + 1, i + 1)
    }
    for _ in 0..n-1 {
        // seq[(pos + dir) as usize] += seq[pos as usize];
        println!("{} {}", pos + 1, pos + dir + 1);
        pos += dir;
    }
    // for i in 0..n {
    //     print!("{} ", seq[i]);
    // }
    // println!("");
}