# 3i Infotech Placement: Sample Questions 446 - 447 of 1245

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## Question 446

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### Describe in Detail

Essay▾

What is the algorithm used in solving the 8 queens problem?

### Explanation

• Backtracking is the type of the algorithm used in solving the 8 Queens problem.
• Considers searching every possible combination in order to solve an optimization problem.
• Also known as depth-first search.

Algorithm of backtracking:

• Boolean solve (Node n)

{

If n is a leaf node

{

If the leaf is goal node, return true

Else return false

}

Else

{

For each child c of n

{

If solve (c) succeeds, return true

}

Return false

}

}

• The algorithm is expressed as a Boolean function.

## Question 447

### Question

MCQ▾

Semaphore is used for

### Choices

Choice (4)

a.

b.

box

c.

synchronization

d.

None of the above

c.

### Explanation

• Semaphore is a simple variable used which uses critical sections to achieve process synchronization in a multi-processing environment.
• Two common semaphores are:
• Counting semaphore which takes non-negative integer values
• Binary semaphore which takes the value .
• If semaphores are implemented using file descriptors. Semaphore creations are not atomic. Thus if two processes try to create, initialize and use a semaphore at the same time, a race condition is created.
• They are thus implemented through interrupts or by using test-set operations to achieve atomicity

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