php面试解决问题
PHP 面试难题解析
在 PHP 面试中，解决问题的能力是至关重要的。面试官会出示一系列问题来评估您解决问题、编写代码和分析解决方案的能力。本文将深入探讨一些常见的 PHP 面试难题，并提供详细的解决方案。
1. 给定一个字符串，找出其中最长的回文子串
php
function longestPalindrome($string) {
$length = strlen($string);
$maxLength = 0;
$start = 0;
$end = 0;
for ($i = 0; $i < $length; $i++) {
for ($j = $i + 1; $j < $length; $j++) {
$substring = substr($string, $i, $j - $i + 1);
if ($substring == strrev($substring) && $j - $i + 1 > $maxLength) {
$maxLength = $j - $i + 1;
$start = $i;
$end = $j;
}
}
}
return substr($string, $start, $maxLength);
}
2. 找出给定数组中两个数的和与目标值最接近的组合
php
function closestSum($array, $target) {
$n = count($array);
$closest = INF;
$result = [];
for ($i = 0; $i < $n; $i++) {
for ($j = $i + 1; $j < $n; $j++) {
$sum = $array[$i] + $array[$j];
$diff = abs($target - $sum);
if ($diff < $closest || $diff == $closest && $sum > $result[0] + $result[1]) {$closest = $diff;
$result = [$array[$i], $array[$j]];
}
}
}
return $result;
}
3. 给定一个二叉树，返回其后序遍历结果
php
function postorderTraversal($root) {
$stack = [];
$result = [];
while ($root || !empty($stack)) {
while ($root) {
$stack[] = $root;
$root = $root->left;
}
$root = $stack[count($stack) - 1];
$stack = array_pop($stack);
$result[] = $root->data;
$root = $root->right;
}
return $result;
}
4. 实现一个斐波那契数列生成器，按需生成下一个数
php
class FibonacciGenerator {
private $previous = 0;
private $current = 1;
public function next(): int {
$next = $this->previous + $this->current;
$this->previous = $this->current;
$this->current = $next;
return $next;
}
}
5. 找出给定数组中缺失的最小正整数
php
function findMissingPositive($array) {
$n = count($array);
$visited = array_fill(0, $n, false);
for ($i = 0; $i < $n; $i++) {
if ($array[$i] <= 0 || $array[$i] > $n) {continue;
}
$visited[$array[$i] - 1] = true;
}
for ($i = 0; $i < $n; $i++) {
if (!$visited[$i]) {
return $i + 1;
}
}
return $n + 1;
}
6. 给定一个正方形矩阵，找到其最大连续子矩阵的和
php
function maxSubmatrixSum($matrix) {
$rows = count($matrix);
$cols = count($matrix[0]);
$maxSum = -INF;
for ($i = 0; $i < $rows; $i++) {
$cumulative = array_fill(0, $cols, 0);
for ($j = $i; $j < $rows; $j++) {
for ($k = 0; $k < $cols; $k++) {
$cumulative[$k] += $matrix[$j][$k];
}
$sum = 0;
$start = 0;
$end = 0;
for ($k = 0; $k < $cols; $k++) {
$sum += $cumulative[$k];
if ($sum > $maxSum) {
$maxSum = $sum;
$start = $i;
$end = $j;
}
if ($sum < 0) {
$sum = 0;
}
}
}
}
return $maxSum;
}
7. 给定一个字符串，找出其最长连续递增子序列
php
function longestIncreasingSubsequence($string) {
$length = strlen($string);
$dp = array_fill(0, $length, 1);
for ($i = 1; $i < $length; $i++) {
for ($j = 0; $j < $i; $j++) {
if ($string[$i] > $string[$j] && $dp[$i] < $dp[$j] + 1) {
$dp[$i] = $dp[$j] + 1;
}
}
}
$maxLen = 0;
$end = 0;
for ($i = 0; $i < $length; $i++) {
if ($dp[$i] > $maxLen) {
$maxLen = $dp[$i];
$end = $i;
}
}
return substr($string, $end - $maxLen + 1, $maxLen);
}
8. 给定一个数组，找出其中两个数的乘积最大的组合
php
function maxProduct($array) {
$n = count($array);
$maxPositive = -INF;
$maxNegative = INF;
$maxProduct = -INF;
for ($i = 0; $i < $n; $i++) {
if ($array[$i] > $maxPositive) {
$maxPositive = $array[$i];
}
if ($array[$i] < $maxNegative && $array[$i] != 0) {
$maxNegative = $array[$i];
}
}
for ($i = 0; $i < $n; $i++) {
for ($j = $i + 1; $j < $n; $j++) {
$product = $array[$i] * $array[$j];
if ($product > $maxProduct) {
$maxProduct = $product;
}
}
}
return $maxProduct;
}
9. 给定一个二叉搜索树，将它转换为双向链表
php
class Node {
public $data;
public $left;
public $right;
public function __construct($data) {
$this->data = $data;
$this->left = null;
$this->right = null;
}
}
function binaryTreeToLinkedList($root) {
if ($root == null) {
return null;
}
$leftHead = binaryTreeToLinkedList($root->left);
$rightHead = binaryTreeToLinkedList($root->right);
$node = new Node($root->data);
if ($leftHead != null) {
$leftTail = $leftHead;
while ($leftTail->right != null) {
$leftTail = $leftTail->right;
}
$leftTail->right = $node;
$node->left = $leftTail;
}
if ($rightHead != null) {
$rightTail = $rightHead;
while ($rightTail->left != null) {
$rightTail = $rightTail->left;
}
$rightTail->left = $node;
$node->right = $rightTail;
}
if ($leftHead == null) {
return $node;
} else {
return $leftHead;
}
}
10. 给定一个数组，找出其中所有子区间的最大和
php
function maxSubarraySums($array) {
$n
