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Data-Structures-Algorithms/segment_tree.cpp at master · joash4000/Data-Structures-Algorithms · GitHub
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#
include
<
bits/stdc++.h
>
using
namespace
std
;
//
Sum of a given segment;
int
getSumUtil
(
int
*st,
int
ss,
int
se,
int
qs,
int
qe,
int
si)
{
//
starting query is less than starting index of the seg and ending query is greater than
//
ending index of the segment, then return the value store at that index;
if
(qs <= ss && qe >= se)
return
st[si];
if
(qs > se || qe < ss)
return
0
;
int
mid = (ss + se) /
2
;
return
getSumUtil
(st, ss, mid, qs, qe,
2
*si+
1
) +
getSumUtil
(st, mid+
1
, se, qs, qe,
2
*si+
2
);
}
void
updateValueUtil
(
int
*st,
int
ss,
int
se,
int
i,
int
diff,
int
si)
{
if
(i < ss || i > se)
return
;
st[si] = st[si] + diff;
if
(ss != se)
{
int
mid = (ss + se) /
2
;
//
Break the segment tree into two parts and compute for each part to get updated segment tree;
updateValueUtil
(st, ss, mid, i, diff,
2
*si+
1
);
updateValueUtil
(st, mid+
1
, se, i, diff,
2
*si+
2
);
}
}
//
Update the value at a particular index in the array;
void
updateValue
(
int
arr[],
int
*st,
int
n,
int
i,
int
val)
{
int
diff = val - arr[i];
arr[i] = val;
updateValueUtil
(st,
0
, n-
1
, i, diff,
0
);
}
//
Calculate sum of a given segment in the array;
int
getSum
(
int
* st,
int
n,
int
qs,
int
qe)
{
//
If starting query is less than 0 or ending query is greater than length of the array
//
or starting query is greater than ending query the program will be terminated;
if
(qs <
0
|| qe > n-
1
|| qe < qs)
return
-
1
;
return
getSumUtil
(st,
0
, n-
1
, qs, qe,
0
);
}
//
Computer power in log(n) time complexity;
int
pown
(
int
a,
int
b)
{
if
(b ==
0
)
return
1
;
if
(b ==
1
)
return
a;
return
pown
(a, b/
2
) *
pown
(a, b - b/
2
);
}
int
constructSTUtil
(
int
arr[],
int
ss,
int
se,
int
*st,
int
si)
{
//
if function goes to leaf node then data value will be value store in that segment in the given array;
if
(ss == se)
{
st[si] = arr[se];
return
arr[ss];
}
int
mid = (ss + se) /
2
;
//
Data value store in a node is the sum of data value store it's two child;
st[si] =
constructSTUtil
(arr, ss, mid, st,
2
*si+
1
) +
constructSTUtil
(arr, mid+
1
, se, st,
2
*si+
2
);
return
st[si];
}
//
Construct the segment tree;
int
*
constructST
(
int
arr[],
int
n)
{
int
x = (
int
)(
ceil
(
log2
(n)));
//
Total no of leaf node in the segment tree;
int
max_size =
2
*
pown
(
2
, x) -
1
;
int
*st =
new
int
[max_size];
//
Construct the segment tree where data value store in a node is the sum of data value store it's two child;
int
val =
constructSTUtil
(arr,
0
, n-
1
, st,
0
);
for
(
int
i =
0
; i < max_size; i++)
cout << st[i] <<
"
"
;
cout << endl;
return
st;
}
int
main
()
{
int
n;
cin>>n;
int
arr[n+
5
];
for
(
int
i =
0
; i < n; i++)
cin>>arr[i];
//
Construct the Segment Tree;
int
*st =
constructST
(arr,n);
//
Get the sum of a given range;
cout <<
getSum
(st, n,
1
,
3
) << endl;
//
Update the value of a particular index in the given array;
updateValue
(arr, st, n,
1
,
10
);
//
Get the sum of a given range;
cout <<
getSum
(st, n,
1
,
3
) << endl;
return
0
;
}
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