/* spaces.c
 * remove spaces from a string in-place - a common interview question
 */
#include <stdio.h>
#include <string.h>

/* Simple implementation that is also efficient */
void remove_spaces1(char *s) {
	int i, j; /* i: input cursor, j: output cursor */
	for(j=i=0;s[i];i++) {
		if(s[i]==' ') continue;
		s[j++]=s[i];
	}
	s[j]=0;
}

/* Second variation of above that is more common to see */
void remove_spaces2(char *s) {
	int i, j; /* i: input cursor, j: output cursor */
	for(j=i=0;s[i];i++) {
		if(s[i]!=' ') {
			s[j++]=s[i];
		}
	}
	s[j]=0;
}

/* very inefficient version that is typical to see in interviews */
void remove_spaces3(char *s) {
	int len;
	while(*s) {
		/* find next space */
		s=strchr(s, ' ');
		if(!s) {
			/* TODO: null terminate */
			return; /* done - no more spaces */
		}

		len=strlen(s);
		memmove(s, s+1, len);
	}
}

/* succinct implementation that implicitly null terminates */
void remove_spaces4(char *s) {
	char *p=s;
	do {
		if(*s!=' ') {
			*p++=*s;
		}
	} while(*s++);
}

/* Simple implementation using two loops */
void remove_spaces5(char *s) {
	int i, j; /* i: input cursor, j: output cursor */
	i=j=0;
	while(s[i]) {
		while(s[i]==' ') i++; /* skip over spaces on input */
		s[j++]=s[i++];
	}
	s[j]=0;
}

/* a very common approach for inexperienced developers who are used to reusing code templates */
void remove_spaces6(char *s) {
	int i, j, len;
	len=strlen(s);
	j=0;
	i=0;
	while(i<=len) { /* usually they do i<len and solve the null termination differently */
		if(s[i]!=' ') {
			s[j]=s[i];
			j++;
			i++;
		} else {
			i++;
		}
	}
}


int main(void) {
	char *testvec[] = {
		"a b c",
		"  a b    c",
		"    ",
		"a ",
		""
	};
	void (*remove_spaces_n[])(char *s) = {
		remove_spaces1,
		remove_spaces2,
		remove_spaces3,
		remove_spaces4,
		remove_spaces5,
		remove_spaces6,
	};
	unsigned i, j;
	for(i=0;i<sizeof testvec/sizeof *testvec;i++) {
		for(j=0;j<6;j++) {
			char buf[strlen(testvec[i])+1];
			memcpy(buf, testvec[i], sizeof buf);
			printf("remove_spaces%d(): \"%s\" -> ", j, buf);
			remove_spaces_n[j](buf);
			printf("\"%s\"\n", buf);
		}
	}
	return 0;
}