50 lines
1.7 KiB
Java
50 lines
1.7 KiB
Java
/**
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* File: binary_search_edge.java
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* Created Time: 2023-08-04
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* Author: krahets (krahets@163.com)
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*/
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package chapter_searching;
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public class binary_search_edge {
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/* 二分搜尋最左一個 target */
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static int binarySearchLeftEdge(int[] nums, int target) {
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// 等價於查詢 target 的插入點
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int i = binary_search_insertion.binarySearchInsertion(nums, target);
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// 未找到 target ，返回 -1
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if (i == nums.length || nums[i] != target) {
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return -1;
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}
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// 找到 target ，返回索引 i
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return i;
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}
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/* 二分搜尋最右一個 target */
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static int binarySearchRightEdge(int[] nums, int target) {
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// 轉化為查詢最左一個 target + 1
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int i = binary_search_insertion.binarySearchInsertion(nums, target + 1);
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// j 指向最右一個 target ，i 指向首個大於 target 的元素
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int j = i - 1;
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// 未找到 target ，返回 -1
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if (j == -1 || nums[j] != target) {
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return -1;
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}
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// 找到 target ，返回索引 j
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return j;
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}
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public static void main(String[] args) {
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// 包含重複元素的陣列
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int[] nums = { 1, 3, 6, 6, 6, 6, 6, 10, 12, 15 };
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System.out.println("\n陣列 nums = " + java.util.Arrays.toString(nums));
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// 二分搜尋左邊界和右邊界
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for (int target : new int[] { 6, 7 }) {
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int index = binarySearchLeftEdge(nums, target);
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System.out.println("最左一個元素 " + target + " 的索引為 " + index);
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index = binarySearchRightEdge(nums, target);
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System.out.println("最右一個元素 " + target + " 的索引為 " + index);
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}
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}
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}
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