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59 lines
2.4 KiB
59 lines
2.4 KiB
/**
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* File: binary_search.java
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* Created Time: 2022-11-25
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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 {
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/* Binary search (double closed interval) */
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static int binarySearch(int[] nums, int target) {
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// Initialize double closed interval [0, n-1], i.e., i, j point to the first element and last element of the array respectively
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int i = 0, j = nums.length - 1;
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// Loop until the search interval is empty (when i > j, it is empty)
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while (i <= j) {
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int m = i + (j - i) / 2; // Calculate midpoint index m
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if (nums[m] < target) // This situation indicates that target is in the interval [m+1, j]
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i = m + 1;
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else if (nums[m] > target) // This situation indicates that target is in the interval [i, m-1]
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j = m - 1;
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else // Found the target element, thus return its index
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return m;
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}
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// Did not find the target element, thus return -1
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return -1;
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}
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/* Binary search (left closed right open interval) */
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static int binarySearchLCRO(int[] nums, int target) {
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// Initialize left closed right open interval [0, n), i.e., i, j point to the first element and the last element +1 of the array respectively
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int i = 0, j = nums.length;
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// Loop until the search interval is empty (when i = j, it is empty)
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while (i < j) {
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int m = i + (j - i) / 2; // Calculate midpoint index m
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if (nums[m] < target) // This situation indicates that target is in the interval [m+1, j)
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i = m + 1;
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else if (nums[m] > target) // This situation indicates that target is in the interval [i, m)
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j = m;
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else // Found the target element, thus return its index
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return m;
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}
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// Did not find the target element, thus return -1
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return -1;
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}
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public static void main(String[] args) {
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int target = 6;
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int[] nums = { 1, 3, 6, 8, 12, 15, 23, 26, 31, 35 };
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/* Binary search (double closed interval) */
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int index = binarySearch(nums, target);
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System.out.println("Index of target element 6 =" + index);
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/* Binary search (left closed right open interval) */
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index = binarySearchLCRO(nums, target);
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System.out.println("Index of target element 6 =" + index);
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}
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}
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