Dutch National Flag Three Way Partition in DSA C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main goal of the Dutch National Flag problem?

To rearrange an array with three types of elements so that all elements of the first type come first, followed by all elements of the second type, and then all elements of the third type.

beginner

Which three pointers are used in the Dutch National Flag algorithm?

Low (start of the array), Mid (current element), and High (end of the array).

intermediate

In the Dutch National Flag algorithm, what happens when the mid element is equal to the first type?

Swap the mid element with the low element, then increment both low and mid pointers.

intermediate

Why does the Dutch National Flag algorithm run in O(n) time?

Because it processes each element at most once by moving pointers without nested loops.

intermediate

What is the role of the high pointer in the Dutch National Flag algorithm?

It marks the boundary for the third type elements and moves backward when swapping elements of the third type.

What does the 'mid' pointer represent in the Dutch National Flag algorithm?

A The current element being examined

B The start of the array

C The end of the array

D The middle element of the array

The 'mid' pointer scans through the array, examining each element to decide its position.

When the mid element is the third type, what action is taken?

A Swap with low and increment low and mid

B Increment mid only

C Swap with high and decrement high

D Do nothing and move on

Swap the mid element with the high element and decrement high to move third type elements to the end.

What is the initial position of the 'high' pointer?

A At the start of the array

B One position before the start

C At the middle of the array

D At the end of the array

The 'high' pointer starts at the last index of the array to track the boundary for the third type.

How many passes through the array does the Dutch National Flag algorithm make?

A Depends on array size

B One pass

C Three passes

D Two passes

It makes a single pass by moving pointers and swapping elements as needed.

Which of these is NOT a pointer used in the Dutch National Flag algorithm?

A Pivot

B Mid

C High

D Low

'Pivot' is not used in this algorithm; only low, mid, and high pointers are used.

Explain the step-by-step process of the Dutch National Flag algorithm.

Think about how the pointers move and how elements are swapped based on their type.

Describe why the Dutch National Flag algorithm is efficient compared to sorting the array normally.

Focus on how many times each element is processed and memory usage.