PHP求连续子数组最大和方法解析

function maxSubArray($nums) {
    if (empty($nums)) return 0;
<pre class="brush:php;toolbar:false;">$currentSum = $nums[0]; // 以当前元素结尾的最大和
$maxSum     = $nums[0]; // 全局最大和

for ($i = 1; $i < count($nums); $i++) {
    // 要么从当前数重新开始，要么接上前一段
    $currentSum = max($nums[$i], $currentSum + $nums[$i]);
    $maxSum     = max($maxSum, $currentSum);
}

return $maxSum;

}

// 示例调用 $arr = [-2, 1, -3, 4, -1, 2, 1, -5, 4]; echo maxSubArray($arr); // 输出：6（对应子数组 [4,-1,2,1]）

function maxSubArrayWithIndex($nums) {
    if (empty($nums)) return ['sum' => 0, 'start' => -1, 'end' => -1];
<pre class="brush:php;toolbar:false;">$currentSum = $nums[0];
$maxSum     = $nums[0];
$start      = 0;
$end        = 0;
$tempStart  = 0;

for ($i = 1; $i < count($nums); $i++) {
    if ($currentSum < 0) {
        $currentSum = $nums[$i];
        $tempStart  = $i;
    } else {
        $currentSum += $nums[$i];
    }

    if ($currentSum > $maxSum) {
        $maxSum = $currentSum;
        $start  = $tempStart;
        $end    = $i;
    }
}

return [
    'sum'   => $maxSum,
    'start' => $start,
    'end'   => $end,
    'subarray' => array_slice($nums, $start, $end - $start + 1)
];

}