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Author: nitish-yb

C++/Data-Structures/Tree/segment tree for max subsequnce(cont) for range queries.cpp

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+#include <bits/stdc++.h>
+using namespace std;
+
+/*Structure that is used to
+store value*/
+struct node
+{
+ int sum,prefixsum;
+ int suffixsum,maxsum;
+};
+
+node tree[4*50010];
+int arr[50010];
+
+/*This function is used to build the
+segment tree*/
+void build(int index,int start,int end)
+{
+ if(start == end)
+ {
+ tree[index].sum = arr[start];
+ tree[index].prefixsum = arr[start];
+ tree[index].suffixsum = arr[start];
+ tree[index].maxsum = arr[start];
+ }
+ else
+ {
+ int mid = (start+end)/2;
+ build(2*index+1,start,mid);
+ build(2*index+2,mid+1,end);
+
+ /*Note how we use the array to access the left
+ and right subtree*/
+ tree[index].sum =
+ tree[2*index+1].sum + tree[2*index+2].sum;
+ tree[index].prefixsum =
+ max(tree[2*index+1].prefixsum,
+ tree[2*index+1].sum + tree[2*index+2].prefixsum);
+ tree[index].suffixsum =
+ max(tree[2*index+2].suffixsum,
+ tree[2*index+2].sum + tree[2*index+1].suffixsum);
+ tree[index].maxsum =
+ max(tree[index].prefixsum,
+ max(tree[index].suffixsum,
+ max(tree[2*index+1].maxsum,
+ max(tree[2*index+2].maxsum,
+ tree[2*index+1].suffixsum
+ +tree[2*index+2].prefixsum
+ )
+ )
+ )
+ );
+ }
+}
+
+/*this function is used to return the result
+for each query*/
+node query(int index,int start,int end,int l,int r)
+{
+ node result;
+ result.sum=result.prefixsum=INT_MIN;
+ result.suffixsum=result.maxsum=INT_MIN;
+
+ if(r<start || end<l)
+ return result;
+ if(l<=start && end<=r)
+ return tree[index];
+
+ int mid = (start+end)/2;
+ if (l > mid)
+ return query(2*index+2, mid+1, end, l, r);
+ if (r <= mid)
+ return query(2*index+1, start, mid, l, r);
+
+ node left = query(2*index+1,start,mid,l,r);
+ node right = query(2*index+2,mid+1,end,l,r);
+
+ result.sum = left.sum + right.sum;
+ result.prefixsum =
+ max(left.prefixsum, left.sum + right.prefixsum);
+ result.suffixsum =
+ max(right.suffixsum, right.sum + left.suffixsum);
+ result.maxsum =
+ max(result.prefixsum,
+ max(result.suffixsum,
+ max(left.maxsum,
+ max(right.maxsum,
+ left.suffixsum + right.prefixsum))));
+ return result;
+}
+
+int main()
+{
+ int n,m,a,b;
+ scanf("%d",&n);
+
+ for(int i=0; i<n; ++i)
+ scanf("%d",&arr[i]);
+
+ build(0,0,n-1);
+
+ scanf("%d",&m);
+
+ for(int i=0; i<m; ++i)
+ {
+ scanf("%d%d",&a,&b);
+ printf("%d\n",query(0,0,n-1,a-1,b-1).maxsum);
+ }
+ return 0;
+}