Interview-Questions/stacksproblems at master · KMuthusamyms/Interview-Questions · GitHub

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// Stock span problem
Code:
#include<stdio.h>
#define MAX 100
int stack[MAX],top=-1;
void push(int x)
{
	stack[++top] = x;
}
void pop()
{
	top = top - 1;
}
int main()
{
	int num, *prices, *span, ind;
	scanf("%d",&num);
	prices=(int*)malloc(sizeof(int)*num);
	span=(int*)malloc(sizeof(int)*num);
	for(ind=0;ind<num;ind++)
		scanf("%d",&prices[ind]);
	span[0] = 1;
	push(0);
	for( ind = 1 ; ind < num ; ind++ )
	{
		while( top != -1 && prices[stack[top]] <= prices[ind] )
			pop();
		span[ind] = ( top == -1 ) ? ind+1 : ind - stack[top];
		push(ind);
	}
	for(ind=0;ind<num;ind++)
		printf("%d ",span[ind]);
	return 0;
}
Time Complexity : As every index is pushed and popped atmost once therefore the
time complexity is O(n)

// Next greater element
Code:
#include<stdio.h>
#define MAX 100
int stack[MAX], top = -1;
void push(int x)
{
	stack[++top] = x;
}
void pop()
{
	top = top - 1;
}
int main()
{
	int num, *array, *greater, index;
	scanf("%d",&num);
	array=(int*)malloc(sizeof(int)*num);
	greater=(int*)malloc(sizeof(int)*num);
	for(index=0;index<num;index++)
		scanf("%d",&array[index]);
	greater[num-1] = -1;
	push(num-1);
	for( index = num-2 ; index >= 0 ;index-- )
	{
		while( top != -1 && array[index] > array[stack[top]] )
			pop();
		greater[index] = ( top == -1 ) ? -1 : array[stack[top]];
		push(index);
	}
	for(index=0;index<num;index++)
		printf("%d ",greater[index]);
	return 0;
}
Time Complexity : As every index is pushed and popped atmost once therefore the
time complexity is O(n)