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Segement_Tree_RMQ.c
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Segement_Tree_RMQ.c
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#include <stdio.h>
#include<stdlib.h>
#include <limits.h>
int min(int x, int y)
{
return (x < y) ? x : y;
}
void build(int *a, int *tree, int start, int end, int treenode)
{
if (start == end)
{
tree[treenode] = a[start];
return;
}
int mid;
mid = (start + end) / 2;
//compute the values in the left and right subtrees
build(a, tree, start, mid, 2 * treenode);
build(a, tree, mid + 1, end, 2 * treenode + 1);
/*store the minimum value in the first and
second half of the interval*/
tree[treenode] = min(tree[2 * treenode], tree[2 * treenode + 1]);
return;
}
int query(int *tree, int start, int end, int l, int r, int treenode)
{
/* if the current interval doesn’t intersect
the query interval return INT_MAX*/
if (start > r || end < l)
{
return INT_MAX;
}
/*if the current interval is included in
the query interval return tree[treenode]*/
if (start >= l && end <= r)
{
return tree[treenode];
}
int mid;
mid = (start + end) / 2;
//return the minimum value
int e = query(tree, start, mid, l, r, 2 * treenode);
int f = query(tree, mid + 1, end, l, r, 2 * treenode + 1);
return min(e, f);
}
int main()
{
int size;
printf("Enter the size of the array: ");
scanf("%d", &size);
int array[size];
int *segTree = (int *)malloc(sizeof(4 * size));
printf("Enter the elements.\n");
for(int i = 0; i < size; i++)
{
scanf("%d", &array[i]);
}
build(array, segTree, 0, size - 1, 1);
int start, end;
printf("Enter the range of the query: ");
scanf("%d %d", &start, &end);
int result = query(segTree, 0, size - 1, start - 1, end - 1, 1);
printf("Minimum value in index range %d to %d is: %d\n", start, end, result);
return 0;
}
/*
Input:
Enter the size of the array.: 5
-7 3 -1 8 1
Enter the range of the query.: 2 5
Output:
Minimum value in index range 2 to 5 is: -1
*/