solve.c

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
void swap(char *a, char *b)
{
	*a ^= *b;
	*b ^= *a;
	*a ^= *b;
}
void reverse(char *str, int s, int t)
{
	int i = s, j = t;
	while (i < j)
		swap(&str[i++], &str[j--]);
}
char *compress(char *s)
{
	if (s == NULL)
		return NULL;
	int n = strlen(s);
	int i = 0;
	int j = n - 1; 
	while (isblank(s[i])) i++;
	while (isblank(s[j])) j--;
	int k;
	for (k = 0; i <= j; ++i) {
		if (!isblank(s[i]) || (i > 0 && !isblank(s[i - 1]))) {
			s[k++] = s[i];
		}
	}
	s[k] = 0;
	return s;
}
void reverseWords(char *s)
{
	if (s == NULL)
		return;
	compress(s);
	int n = strlen(s);
	if (n <= 1)
		return;
	reverse(s, 0, n - 1);
	int pos = 0;
	for (int i = 0; i < n; ++i) {
		if (isblank(s[i])) {
			reverse(s, pos, i - 1);
			pos = i + 1;
		}
	}
	reverse(s, pos, n - 1); // The last word
}
int main(int argc, char **argv)
{
	char s1[] = "the sky is blue";
	char s2[] = "     the    sky is    blue      ";
	char s3[] = " ";
	char s4[] = "pz! .xwy.,cga. vua frjrmcjf, xxw'izz vgthvpfhl sldudifok wvls orujxroi w. oo c?ymxlptr ff'?rh bsjjoyjwvx tj pqv.zlq ,jlu',j dg izq.fo wtvwqn teual jnsv.a .oclyrvg tkgag'a' !wsz?sclc pvhl.ypq vyin cn?z,kxg , u l?l glr zf'hew l'wmi .nlvgr u zfwzra? ot!emgg. rg,'.d.kp fn vat ba.myfqxe znzdrhh xjeubr taztndst v nep?bs .,pwin. e pi";
	reverseWords(s1);
	reverseWords(s2);
	reverseWords(s3);
	reverseWords(s4);
	printf("'%s'\n", s1);
	printf("'%s'\n", s2);
	printf("'%s'\n", s3);
	printf("'%s'\n", s4);
	return 0;
}