this works in O(n) as first reverse all the sentence....then
reverse each word....


#include<iostream.h>
#include<conio.h>
#include<string.h>

char a[50];

void wrd_reverse()
{
void str_rev(int start_index,int len);
int t=strlen(a);
str_rev(0,t);
int i=0;int st_indx=0;int count=0;
int size;
while(a[i]!='\0')
	{
	if(a[i]!=' ')
	count++;
	else
	{

	size=count;
	str_rev(st_indx,size);
	count=0;
	st_indx=i+1;
	}
	i++;
	}
size=count;
str_rev(st_indx,size);

}

void str_rev(int start_index,int len)
{
int sft=start_index;
int lenm=len/2;
len--;
for(int i=0;i<lenm;i++)
	{
	a[sft+i]=a[sft+i]+a[(sft+len)-i];
	a[(sft+len)-i]=a[sft+i]-a[(sft+len)-i];
	a[sft+i]=a[sft+i]-a[(sft+len)-i];
	}
}

int main(){
cin.getline(a,40);
void wrd_reverse();
wrd_reverse();
cout.write(a,40);
return 0;

}