Correct stride pseudocode in p27 (#240)

Author: dunnoconnor

book/i18n/ko/src/puzzle_27/puzzle_27.md

@@ -48,10 +48,12 @@ GPU 스레드 블록 (128 스레드, 4개 또는 2개 워프, 하드웨어 조
 # 복잡한 블록 전체 리덕션 (기존 방식 - Puzzle 12에서):
 shared_memory[local_i] = my_value
 barrier()
-for stride in range(64, 0, -1):
+stride = 64
+while stride > 0:
     if local_i < stride:
         shared_memory[local_i] += shared_memory[local_i + stride]
     barrier()
+    stride //= 2
 if local_i == 0:
     output[block_idx.x] = shared_memory[0]
 
@@ -81,10 +83,12 @@ if local_i == 0:
 shared_memory[local_i] = my_value
 barrier()
 # 스트라이드 기반 인덱싱을 사용한 트리 리덕션...
-for stride in range(64, 0, -1):
+stride = 64
+while stride > 0:
     if local_i < stride:
         shared_memory[local_i] += shared_memory[local_i + stride]
     barrier()
+    stride //= 2
 ```
 
 ### **중간 단계: 워프 프로그래밍 (Puzzle 24)**

book/src/puzzle_27/puzzle_27.md

@@ -46,10 +46,12 @@ Learn the complete parallel programming toolkit from `gpu.primitives.block`:
 # Complex block-wide reduction (traditional approach - from Puzzle 12):
 shared_memory[local_i] = my_value
 barrier()
-for stride in range(64, 0, -1):
+stride = 64
+while stride > 0:
     if local_i < stride:
         shared_memory[local_i] += shared_memory[local_i + stride]
     barrier()
+    stride //= 2
 if local_i == 0:
     output[block_idx.x] = shared_memory[0]
 
@@ -79,10 +81,12 @@ Complex but educational - explicit shared memory, barriers, and tree reduction:
 shared_memory[local_i] = my_value
 barrier()
 # Tree reduction with stride-based indexing...
-for stride in range(64, 0, -1):
+stride = 64
+while stride > 0:
     if local_i < stride:
         shared_memory[local_i] += shared_memory[local_i + stride]
     barrier()
+    stride //= 2
 ```
 
 ### **The intermediate step: Warp programming (Puzzle 24)**