hello-algo/codes/kotlin/chapter_searching/binary_search_edge.kt

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/**
* File: binary_search_edge.kt
* Created Time: 2024-1-25
* Author: curtishd (1023632660@qq.com)
*/
package chapter_searching
/* 二分查找最左一个 target */
fun binarySearchLeftEdge(nums: IntArray, target: Int): Int {
// 等价于查找 target 的插入点
val i = binarySearchInsertion(nums, target)
// 未找到 target ,返回 -1
if (i == nums.size || nums[i] != target) {
return -1
}
// 找到 target ,返回索引 i
return i
}
/* 二分查找最右一个 target */
fun binarySearchRightEdge(nums: IntArray, target: Int): Int {
// 转化为查找最左一个 target + 1
val i = binarySearchInsertion(nums, target + 1)
// j 指向最右一个 target i 指向首个大于 target 的元素
val j = i - 1
// 未找到 target ,返回 -1
if (j == -1 || nums[j] != target) {
return -1
}
// 找到 target ,返回索引 j
return j
}
/* Driver Code */
fun main() {
// 包含重复元素的数组
val nums = intArrayOf(1, 3, 6, 6, 6, 6, 6, 10, 12, 15)
println("\n数组 nums = ${nums.contentToString()}")
// 二分查找左边界和右边界
for (target in intArrayOf(6, 7)) {
var index = binarySearchLeftEdge(nums, target)
println("最左一个元素 $target 的索引为 $index")
index = binarySearchRightEdge(nums, target)
println("最右一个元素 $target 的索引为 $index")
}
}