20345번 - XOR Sort 서브태스크스페셜 저지다국어

문제

You are given an integer S and an array A consisting of N non-negative integers, indexed from 1. You are allowed to perform the following operation on it: choose any index i (1 ≤ i ≤ N), choose one of its neighbors j (1 ≤ j ≤ N, either j = i − 1 or j = i + 1) and replace A_i with (A_i ⊕ A_j) where ⊕ is the bitwise XOR operation.

You can see the definition of XOR at the end of the statement.

Your goal is to transform A into a sorted array:

• If S = 1 then the final array must be strictly increasing, i.e. A_i < A_i+1 for 1 ≤ i < N
• If S = 2 then the final array must be non-decreasing, i.e. A_i ≤ A_i+1 for 1 ≤ i < N

Find any sequence of operations that achieves your goal.

You aren’t required to minimize the number of operations as long as their amount doesn’t exceed 40000.

입력

First line contains two integers: N and S

Next line contains N integers: elements of A

출력

First line of output should contain one integer K (0 ≤ K ≤ 40000) - the number of operations.

Next K lines should contain two integers each, describing operations in chronological order: the first integer is an index i of the element which is being replaced and the second one is an index j of another element involved in the operation.

제한

• 1 ≤ S ≤ 2
• 2 ≤ N ≤ 1000
• 0 ≤ A_i < 2²⁰

서브태스크

힌트

First example output explanation: [3, 2, 8, 4, 1] -> [1, 2, 8, 4, 1] -> [1, 2, 8, 12, 1] -> [1, 2, 8, 12, 13]

Second example output explanation: [4, 4, 2, 0, 1] -> [4, 4, 6, 0, 1] -> [4, 4, 6, 6, 1] -> [4, 4, 6, 6, 7]

When performing XOR operation between a and b bits the result will be 0 if a=b and 1 otherwise.

When performing bitwise XOR operation between integers a and b, XOR results will be carried out for each of the corresponding bits:

• 75 ⊕ 29 = 1001011₂ ⊕ 0011101₂ = 1010110₂ = 86

In C/C++/Java you can use the "^" operator to perform XOR.