46 lines
1.5 KiB
JavaScript
46 lines
1.5 KiB
JavaScript
/**
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* File: binary_search_edge.js
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* Created Time: 2023-08-22
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* Author: Gaofer Chou (gaofer-chou@qq.com)
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*/
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const { binarySearchInsertion } = require('./binary_search_insertion.js');
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/* Binary search for the leftmost target */
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function binarySearchLeftEdge(nums, target) {
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// Equivalent to finding the insertion point of target
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const i = binarySearchInsertion(nums, target);
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// Did not find target, thus return -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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// Found target, return index i
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return i;
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}
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/* Binary search for the rightmost target */
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function binarySearchRightEdge(nums, target) {
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// Convert to finding the leftmost target + 1
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const i = binarySearchInsertion(nums, target + 1);
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// j points to the rightmost target, i points to the first element greater than target
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const j = i - 1;
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// Did not find target, thus return -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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// Found target, return index j
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return j;
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}
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/* Driver Code */
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// Array with duplicate elements
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const nums = [1, 3, 6, 6, 6, 6, 6, 10, 12, 15];
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console.log('\nArray nums =' + nums);
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// Binary search for left and right boundaries
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for (const target of [6, 7]) {
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let index = binarySearchLeftEdge(nums, target);
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console.log('The leftmost index of element ' + target + ' is ' + index);
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index = binarySearchRightEdge(nums, target);
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console.log('The rightmost index of element ' + target + ' is ' + index);
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}
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