102 lines
2.0 KiB
PHP
102 lines
2.0 KiB
PHP
<?php
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/**
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* 二分查找 查找=find的元素
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* @param array $numbers
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* @param [type] $find
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*
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* @return void
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* @date 2018/11/26
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* @author yuanliandu
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*/
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function binarySearch(array $numbers, $find)
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{
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$low = 0;
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$high = count($numbers) - 1;
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return search($numbers, $low, $high, $find);
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}
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function search(array $numbers, $low, $high, $find)
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{
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/**
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* notice1 循环退出条件
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*/
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if ($low > $high) {
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return -1;
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}
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/**
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* notice2 mid计算
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*/
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$mid = $low + (($high - $low) >> 1);
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if ($numbers[$mid] > $find) {
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//notice3 high值更新
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return search($numbers, $low, $mid -1, $find);
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} elseif ($numbers[$mid] < $find) {
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//notice4 low值更新
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return search($numbers, $mid + 1, $high, $find);
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} else {
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return $mid;
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}
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}
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/**
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* 求数字的平方根，保留6位小数
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* @param [type] $number
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*
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* @return void
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* @date 2018/11/26
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* @author yuanliandu
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*/
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function squareRoot($number)
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{
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if ($number < 0) {
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return -1;
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} elseif ($number < 1) {
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$min = $number;
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$max = 1;
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} else {
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$min = 1;
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$max = $number;
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}
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$mid = $min + ($max - $min) / 2;
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while (getDecimalPlaces($mid) < 6) {
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$square = $mid * $mid;
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if ($square > $number) {
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$max = $mid;
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} elseif ($square == $number) {
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return $mid;
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} else {
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$min = $mid;
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}
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$mid = $min + ($max - $min) / 2;
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}
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return $mid;
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}
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/**
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* 计算数字小数点后有几位数字
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* @param [type] $number
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*
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* @return void
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* @date 2018/11/27
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* @author yuanliandu <yuanliandu@qq.com>
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*/
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function getDecimalPlaces($number)
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{
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$temp = explode('.', $number);
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if (isset($temp[1])) {
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return strlen($temp[1]);
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}
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return 0;
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}
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// 测试二分查找给定值
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$numbers = [0, 1, 2, 3, 3, 4, 5, 6, 7, 9];
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$find = 1;
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var_dump(binarySearch($numbers,$find));
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//测试求平方根
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var_dump(squareRoot(3)); |