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Two-way merge sort

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Two-way merge sort

Two-way merge sort sits in the roll list. Riya’s job is names A→Z. Write that first.

Keep Two-way merge sort small. Riya should finish names A→Z in a few lines, not a 40-line dump.

Without Two-way merge sort, the roll list gets messy and names A→Z is hard to trust.

Riya ships Two-way merge sort in the roll list. That is the use case worth saying.

Two-way merge sort miss — unstable sort when equal keys matter. Fix it before you talk about advanced DSA.

Two-way merge sort is not a lonely heading. Riya ties it to names A→Z.

One breath for Two-way merge sort, then names A→Z, then unstable sort when equal keys matter. Sit down.

Exam tip

Board: names A→Z. Dry-run Two-way merge sort. Name the trap: unstable sort when equal keys matter.

Example

def merge_sort(arr):
    if len(arr) <= 1:
        return arr
    mid = len(arr) // 2
    left = merge_sort(arr[:mid])
    right = merge_sort(arr[mid:])
    out, i, j = [], 0, 0
    while i < len(left) and j < len(right):
        if left[i] <= right[j]:
            out.append(left[i]); i += 1
        else:
            out.append(right[j]); j += 1
    return out + left[i:] + right[j:]

print(merge_sort([5, 1, 4, 2]))

Two-way merge sort — merge sort divides the array, sorts halves, then merges — O(n log n).

Short notes

DefTwo-way merge sort — Riya uses it for names A→Z in the roll list.
RuleTwo-way merge sort → n log n vs n².
RememberTwo-way merge sort + a dry-run table (the roll list).
UseTwo-way merge sort in the roll list (names A→Z).
TrapTwo-way merge sort — unstable sort when equal keys matter.
ExTwo-way merge sort → names A→Z.

def merge_sort(arr): if len(arr) <= 1: return arr mid = len(arr) // 2 left = merge_sort(arr[:mid]) right = merge_sort(arr[mid:]) out, i, j = [], 0, 0 while i < len(left) and j < len(right): if left[i] <= right[j]: out.append(left[i]); i += 1 else: out.append(right[j]); j += 1 return out + left[i:] + right[j:] print(merge_sort([5, 1, 4, 2]))

Two-way merge sort

Example

Short notes

Questions

Two-way merge sort

Example

Short notes

Questions