【数据结构】Binary_Indexed_Tree

点修改 段求和

 1 var
    a:array[1..100000] of integer;
    t:array[1..100000] of longint;
    i,j,n:integer;
function lowbit(x:integer):integer;
begin
    exit(x and (-x));
end;
procedure edit(k:integer;x:longint);
var
    i,temp:integer;
begin
    i:=k;
    temp:=a[k]-x;
    while i<=n do
    begin
        inc(t[i],temp);
        i:=i+lowbit(i);
    end;
end;
function sum(k:integer):longint;
var
    i:integer;
begin
    i:=k;
    while i>0 do
    begin
        inc(sum,t[i]);
        i:=lowbit(i);
    end;
end;
begin
    for i:=1 to n do
    begin
        for j:=i-lowbit(i)+1 to i do inc(t[i],a[j]);
    end;
end.