/**
* Created by PhpStorm.
* User: lunweiwei
* Date: 16/8/30
* Time: 上午11:15
*/
$source = [-1, 1, 2, -5, 7];
function maxSub($source = [])
{
$max_item = max($source);
if ($max_item <= 0) {
return $max_item;
}
$max_sub_sum = 0;
$sum = 0;
$count = count($source);
for ($i = 0; $i < $count; $i++) {
if ($sum <= 0) {
$sum = $source[$i];
} else {
$sum += $source[$i];
}
if ($max_sub_sum < $sum) {
$max_sub_sum = $sum;
}
}
return $max_sub_sum;
}
$max_sub_sum = maxSub($source);
var_dump($max_sub_sum);
// 太复杂，看不懂
// 规则：
// （1）任何可能产生最大和的子序列，首尾元素只能是正值。
// （2）如果某个序列和为负值，那么以这个序列开始的所有序列都不可能出现最大和，故忽略掉。
function maxSub2($arr)
{
$n = count($arr);
$thisSum = $maxSum = 0;
$s = $e = 0;
for ($j = 0; $j < $n; $j++) {
$thisSum += $arr[$j];
#echo 'j: ', $j, "\n";
#echo 'thisSum: ', $thisSum, "\n";
#echo 'maxSum: ', $maxSum, "\n";
#echo '---------------------', "\n";
if ($thisSum > $maxSum) {
$maxSum = $thisSum;
$e = $j;
} elseif ($thisSum < 0) {
$thisSum = 0;
$e = $s = $j + 1;
}
}
echo __FUNCTION__, "({$s}~{$e}): ", $maxSum, "\n";
}
$arr = [4, -3, 5, -2, -1, 2, 6, -2];
$arr = [-2, 1, -3, 4, -1, 2, 1, -5, 4];
#$arr = [ 4, 3, 5 ];
echo json_encode($arr), "\n";
maxSub($arr);
maxSub2($arr);