function InversePairs($data)
{
$num=0;
$temp=array();
mergeSort($data,0,count($data)-1,$temp,$num);
$num%=1000000007;
return $num;
}
//1.利用分治法思想,递归的切分排序元素
function mergeSort(&$A,$left,$right,$temp,&$num){
//2.最左只能小于最右,等于的时候就一个元素,大于是不可能的
if($left<$right){
//3.获取中间的元素
$mid=intval(($left+$right)/2);
//4.递归左半区
mergeSort($A,$left,$mid,$temp,$num);
//5.递归右半区
mergeSort($A,$mid+1,$right,$temp,$num);
//6.合并两个有序数组为一个有序数组
merge($A,$left,$mid,$right,$temp,$num);
}
}
function merge(&$A,$left,$mid,$right,$temp,&$num){
//7.左堆起始
$i=$left;
//8.右堆起始
$j=$mid+1;
//9.临时数组起始
$t=0;
//10.左右堆数组都没到末尾
while($i<=$mid && $j<=$right){
//11.左堆小于等于右堆时
if($A[$i]<$A[$j]){
//12.左堆赋给临时数组,索引加1
$temp[$t++]=$A[$i++];
}else{
$num+=$mid-$i+1;
//13.右堆赋给临时数组,索引加1
$temp[$t++]=$A[$j++];
}
}
//14.左堆剩余的全部加进临时数组
while($i<=$mid){
$temp[$t++]=$A[$i++];
}
//15.右堆剩余全部加进临时数组
while($j<=$right){
$temp[$t++]=$A[$j++];
}
//16.临时数组的元素重新赋回原数组
for($i=0;$i<$t;$i++){
$A[$left+$i]=$temp[$i];
}
}
$A=[364,637,341,406,747,995,234,971,571,219,993,407,416,366,315,301,601,650,418,355,460,505,360,965,516,648,727,667,465,849,455,181,486,149,588,233,144,174,557,67,74
6,550,474,162,268,142,463,221,882,576,604,739,288,569,256,936,275,401,497,82,935,983,583,523,697,478,147,795,380,973,958,115,773,870,259,655,446,863,735,784,3,671,43
3,630,425,930,64,266,235,187,284,665,874,80,45,848,38,811,267,575];
$m=InversePairs($A);
var_dump($m);