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"""
File: binary_search_edge.py
Created Time: 2023-08-04
Author: krahets (krahets@163.com)
"""
import sys
from pathlib import Path
sys . path . append ( str ( Path ( __file__ ) . parent . parent ) )
from binary_search_insertion import binary_search_insertion
def binary_search_left_edge ( nums : list [ int ] , target : int ) - > int :
""" 二分搜尋最左一個 target """
# 等價於查詢 target 的插入點
i = binary_search_insertion ( nums , target )
# 未找到 target ，返回 -1
if i == len ( nums ) or nums [ i ] != target :
return - 1
# 找到 target ，返回索引 i
return i
def binary_search_right_edge ( nums : list [ int ] , target : int ) - > int :
""" 二分搜尋最右一個 target """
# 轉化為查詢最左一個 target + 1
i = binary_search_insertion ( nums , target + 1 )
# j 指向最右一個 target ，
j = i - 1
# 未找到 target ，返回 -1
if j == - 1 or nums [ j ] != target :
return - 1
# 找到 target ，返回索引 j
return j
""" Driver Code """
if __name__ == " __main__ " :
# 包含重複元素的陣列
nums = [ 1 , 3 , 6 , 6 , 6 , 6 , 6 , 10 , 12 , 15 ]
print ( f " \n 陣列 nums = { nums } " )
# 二分搜尋左邊界和右邊界
for target in [ 6 , 7 ] :
index = binary_search_left_edge ( nums , target )
print ( f " 最左一個元素 { target } 的索引為 { index } " )
index = binary_search_right_edge ( nums , target )
print ( f " 最右一個元素 { target } 的索引為 { index } " )
