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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 :
""" 二分查找最左一个 target """
# 等价于查找 target 的插入点
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 :
""" 二分查找最右一个 target """
# 转化为查找最左一个 target + 1
i = binary_search_insertion ( nums , target + 1 )
# j 指向最右一个 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__ " :
# 包含重复元素的数组
nums = [ 1 , 3 , 6 , 6 , 6 , 6 , 6 , 10 , 12 , 15 ]
print ( f " \n 数组 nums = { nums } " )
# 二分查找左边界和右边界
for target in [ 6 , 7 ] :
index = binary_search_left_edge ( nums , target )
print ( f " 最左一个元素 { target } 的索引为 { index } " )
index = binary_search_right_edge ( nums , target )
print ( f " 最右一个元素 { target } 的索引为 { index } " )
