91 lines
2.4 KiB
JavaScript
91 lines
2.4 KiB
JavaScript
/**
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* 二分查找
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*
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* Author: nameczz
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*/
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// 查找第一个等于给定值
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const biaryFindFirst = (sortedArr, target) => {
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if (sortedArr.length === 0) return -1
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let low = 0
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let high = sortedArr.length - 1
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while (low <= high) {
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const mid = Math.floor((low + high) / 2)
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if (target < sortedArr[mid]) {
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high = mid - 1
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} else if (target > sortedArr[mid]) {
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low = mid + 1
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} else {
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if (mid === 0 || sortedArr[mid - 1] < target) return mid
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high = mid - 1
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}
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}
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return -1
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}
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// 查找最后一个相等的数
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const biaryFindLast = (sortedArr, target) => {
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if (sortedArr.length === 0) return -1
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let low = 0
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let high = sortedArr.length - 1
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while (low <= high) {
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const mid = Math.floor((low + high) / 2)
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if (target < sortedArr[mid]) {
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high = mid - 1
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} else if (target > sortedArr[mid]) {
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low = mid + 1
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} else {
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if (mid === sortedArr.length - 1 || sortedArr[mid + 1] > target) return mid
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low = mid + 1
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}
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}
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return -1
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}
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// 查找第一个大于等于给定值的元素
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const biaryFindFistBig = (sortedArr, target) => {
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if (sortedArr.length === 0) return -1
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let low = 0
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let high = sortedArr.length - 1
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while (low <= high) {
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const mid = Math.floor((low + high) / 2)
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if (target <= sortedArr[mid]) {
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if (mid === 0 || sortedArr[mid - 1] < target) return mid
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high = mid - 1
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} else {
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low = mid + 1
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}
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}
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return -1
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}
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// 查找最后一个小于等于给定值的元素
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const biaryFindLastSmall = (sortedArr, target) => {
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if (sortedArr.length === 0) return -1
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let low = 0
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let high = sortedArr.length - 1
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while (low <= high) {
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const mid = Math.floor((low + high) / 2)
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if (target < sortedArr[mid]) {
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high = mid - 1
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} else {
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if (mid === sortedArr.length - 1 || sortedArr[mid + 1] >= target) return mid
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low = mid + 1
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}
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}
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return -1
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}
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const arr = [1, 2, 3, 4, 4, 4, 4, 4, 6, 7, 8, 8, 9]
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const first = biaryFindFirst(arr, 4)
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console.log(`FindFirst: ${first}`)
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const last = biaryFindLast(arr, 4)
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console.log(`FindLast: ${last}`)
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const FisrtBig = biaryFindFistBig(arr, 5)
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console.log(`FindFisrtBig: ${FisrtBig}`)
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const LastSmall = biaryFindLastSmall(arr, 4)
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console.log(`FindLastSmall: ${LastSmall}`)
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