Sort 0s, 1s and 2s (Dutch National Flag Problem)

Sort 0s, 1s and 2s (Dutch National Flag Problem) Problem Statement Given an array arr[] containing only 0s, 1s, and 2s, sort the array in ascending order. Constraint: You cannot use built-in sort functions. Examples Input: arr = [0, 1, 2, 0, 1, 2] Output: [0, 0, 1, 1, 2, 2] Input: arr = [0, 1, 1, 0, 1, 2, 1, 2, 0, 0, 0, 1] Output: [0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 2, 2] ________________________________________Objective • Sort array without using sort() • Use efficient algorithm (one pass preferred) • Maintain constant extra space Approach 1: Counting Method Idea • Count number of 0s, 1s, and 2s • Overwrite the array accordingly Python Code arr = [0, 1, 2, 0, 1, 2] count0 = arr.count(0) count1 = arr.count(1) count2 = arr.count(2) arr = [0]*count0 + [1]*count1 + [2]*count2 print(arr) Complexity • Time: O(n) • Space: O(1) (ignoring output array) Approach 2: Dutch National Flag Algorithm (Best Solution) Idea Use three pointers: • low → position for 0 • mid → current element • high → position