73 lines
1.3 KiB
PHP
73 lines
1.3 KiB
PHP
<?php
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/*
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* 归并排序
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*/
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$arr = [4, 5, 6, 1, 3, 2];
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$length = count($arr);
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$p = 0;
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$r = $length - 1;
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$result = mergeSort($arr, $p, $r);
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var_dump($result);
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function mergeSort(array $arr, $p, $r)
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{
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return mergeSortRecursive($arr, $p, $r);
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}
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// 递归调用函数
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function mergeSortRecursive(array $arr, $p, $r)
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{
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// 递归终止条件
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if ($p >= $r) {
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return [$arr[$r]];
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}
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// 取 p 到 r 之间的中间位置 q
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$q = (int)(($p + $r) / 2);
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// 分治递归
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$left = mergeSortRecursive($arr, $p, $q);
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$right = mergeSortRecursive($arr, $q + 1, $r);
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return merge($left, $right);
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}
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// 合并
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function merge(array $left, array $right)
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{
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$tmp = [];
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$i = $j = 0;
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$leftLength = count($left);
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$rightLength = count($right);
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do {
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if ($left[$i] <= $right[$j]) {
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$tmp[] = $left[$i++];
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} else {
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$tmp[] = $right[$j++];
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}
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} while ($i < $leftLength && $j < $rightLength);
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$start = $i;
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$end = $leftLength;
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$copyArr = $left;
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// 判断哪个子数组中有剩余的数据
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if ($j < $rightLength) {
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$start = $j;
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$end = $rightLength;
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$copyArr = $right;
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}
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// 将剩余的数据拷贝到临时数组 tmp
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do {
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$tmp[] = $copyArr[$start++];
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} while ($start < $end);
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return $tmp;
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} |