數組

public class Solution{

    class SegmentTreeNode{
      public int start,end;
      public int count;
      public SegmentTreeNode left,right;
      public SegmentTreeNode(int short,int end,int count){
       this.start =start;
       this.end =end;
       this.count =count;
       this.left =this.right =null;
      }
}
SegmentTreeNode root;
public SegmentTreeNode build(int start,int end){
    if(start>end){
        return null;
    }

  SegmentTreeNode root =new SegmentTreeNode(start,end,0);
    if(start!=end){
        int mid =(start+end)/2;
        root.left =build(start,mid);
        root.right =build(mid+1,end);
    } else{
        root.count =0;
    }
    return root;
}
public int querySegmentTree(SegmentTreeNode root,int start,int end){
    if(start==root.start&&root.end==end){
        return root.count;
    }
    int mid =(count.start+root.end)/2;
    int leftcount =0,rightcount =0
    //左子區
    if(start<=mid){
        if(mid<end){
            leftcount =querySegmentTree(root.left,start,mid);
        }else{
            leftcount =querySegmentTree(root.left,start,end);
        }
    }
    //右子區
    if(mid<end){
        if(start<=mid){
            rightcount =querySegmentTree(root.right,mid+1,end);
        }else{
            rightcount =querySegmentTree(root.right,start,end);
        }
    }
    //else就是不相交
    return leftcount+rightcount;

}
public void modifySegmeniTree(SegmentTreeNode root,int index,int value){
    if(root.start ==index&&root.end==index){
        root.count+=value;
        return;
    }
    //查詢
    int mid =(root.start+root.end)/2;
    if(root.start<=index&&index<=mid){
        modifySegmeniTree(root.left,index,value);
    }
    if(mid<index&&index<=root.end){
        modifySegmeniTree(root.right,index,value);
    }
    //更新
    root.count==root.left.count+root.right.count;
}
public ArrayList<Integer> countOfSmallerNumberII(int []A){
    root =build(0,10000);
    ArrayList<Integer>ans =new ArrayList<Integer>();
    int res;
    for(int i=0;i<A,length;i++){
        res=0;
    if(A[i]>0){
        res=querySegmentTree(root,0,A[i]-1);
    }
    modifySegmeniTree(root,A[i],1);
    ans.add(res);
    }
   return ans;
  }
}