From beac4bc8129869d82a6bc49957464c88e50ccfb9 Mon Sep 17 00:00:00 2001
From: zlg <zlg@zlg.space>
Date: Tue, 4 Aug 2015 01:20:56 -0700
Subject: Solve Exercise 6-03: Word cross-referencing

---
 ch6/6-03_line_location.c | 190 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 190 insertions(+)
 create mode 100644 ch6/6-03_line_location.c

diff --git a/ch6/6-03_line_location.c b/ch6/6-03_line_location.c
new file mode 100644
index 0000000..9a22c81
--- /dev/null
+++ b/ch6/6-03_line_location.c
@@ -0,0 +1,190 @@
+#include <stdio.h>
+#include <string.h>
+#include <ctype.h>
+#include <stdlib.h>
+
+/* The C Programming Language: 2nd Edition
+ *
+ * Exercise 6-3: Write a cross-referencer that prints a list of all words in a
+ * document, and, for each word, a list of the line numbers on which it occurs.
+ * Remove noise words like "the", "and", and so on.
+ *
+ * Notes: The trick to this is to pare down a few functions from 6-2, then add
+ * a separate struct to be part of the tnode struct. I opted for a linked list
+ * of line numbers and some recursion. getline could have been used, and might
+ * have been slightly simpler, but this gets the job done. There's certainly
+ * some room for better word detection, and the tlist structure could probably
+ * be something that's not O(n), but this is Category-0 so who cares? :)
+ */
+
+#define BUFSIZE 1000
+#define MAXWORD 100
+#define DEF_PRE_LEN 4
+
+struct tlist {
+	struct tlist *next;
+	int num;
+};
+
+struct tnode {
+	char *word;
+	struct tlist *lines;
+	struct tnode *left;
+	struct tnode *right;
+};
+
+char buf[BUFSIZE];
+int bufp = 0;
+int minlen;
+int line_nr = 1;
+
+int getch(void);
+void ungetch(int);
+int getword(char *, int);
+struct tnode *addtree(struct tnode *, char *, int);
+void addlist(struct tlist *, int);
+void treeprint(struct tnode *);
+void listprint(struct tlist *);
+struct tnode *talloc(void);
+struct tlist *lalloc(void);
+char *mystrdup(char *);
+
+int main(int argc, char *argv[]) {
+	switch (argc) {
+		case 1:
+			minlen = DEF_PRE_LEN;
+			break;
+		case 2:
+			minlen = strtol(argv[1], NULL, 10);
+			break;
+		default:
+			printf("Too many arguments.\n");
+			return 1;
+	}
+	struct tnode *root;
+	char word[MAXWORD];
+	root = NULL;
+	while (getword(word, MAXWORD) != EOF) {
+		/* Only add the words we need to the tree */
+		if (isalpha(word[0]) && strlen(word) > minlen) {
+			root = addtree(root, word, line_nr);
+		}
+	}
+	if (root == NULL) {
+		printf("No words at that length or greater were found.\n");
+		return 1;
+	} else {
+		treeprint(root);
+		return 0;
+	}
+}
+
+int getword(char *word, int lim) {
+	int c;
+	char *w = word;
+	while (isspace(c = getch())) {
+		if (c == '\n') {
+			line_nr++;
+		}
+	}
+	if (c == EOF) {
+		return EOF;
+	}
+	if (c != EOF) {
+		*w++ = c;
+	}
+	for ( ; --lim > 0; w++) {
+		if (!isalpha(*w = getch())) {
+			ungetch(*w);
+			break;
+		}
+	}
+	*w = '\0';
+	return word[0];
+}
+
+int getch(void) {
+	return (bufp > 0) ? buf[--bufp] : getchar();
+}
+
+void ungetch(int c) {
+	if (bufp >= BUFSIZE) {
+		printf("ungetch: Too many characters.\n");
+	} else {
+		buf[bufp++] = c;
+	}
+}
+
+struct tnode *addtree(struct tnode *p, char *w, int pos) {
+	int cond;
+	if (p != NULL) {
+		if ((cond = strcmp(w, p->word)) == 0) {
+			addlist(p->lines, pos);
+		} else if (cond < 0) {
+			p->left = addtree(p->left, w, pos);
+		} else if (cond > 0) {
+			p->right = addtree(p->right, w, pos);
+		}
+	} else {
+		p = talloc();
+		p->lines = lalloc();
+		p->word = mystrdup(w);
+		/* Add to the list of lines */
+		(p->lines)->num = pos;
+		(p->lines)->next = NULL;
+		p->left = p->right = NULL;
+	}
+	return p;
+}
+
+void addlist(struct tlist *l, int pos) {
+	/* Follow the list until we reach the end */
+	while (l->next != NULL) {
+		l = l->next;
+	}
+	/* Don't add a line number if the numbers match! */
+	if (l->num == pos) {
+		return;
+	}
+	/* This won't happen unless l->next is NULL, meaning we've reached the end of the list. */
+	struct tlist *newline = lalloc();
+	newline->num = pos;
+	newline->next = NULL;
+	/* Let's add to it now */
+	l->next = newline;
+}
+
+void treeprint(struct tnode *p) {
+	if (p != NULL) {
+		treeprint(p->left);
+		printf("%-20s  ", p->word);
+		listprint(p->lines);
+		treeprint(p->right);
+	}
+}
+
+void listprint(struct tlist *list) {
+	printf("%3d ", list->num);
+	if (list->next != NULL) {
+		listprint(list->next);
+	} else {
+		printf("\n");
+	}
+}
+
+struct tnode *talloc(void) {
+	return (struct tnode *) malloc(sizeof(struct tnode));
+}
+
+struct tlist *lalloc(void) {
+	return (struct tlist *) malloc(sizeof(struct tlist));
+}
+
+char *mystrdup(char *s) {
+	char *p;
+	p = (char *) malloc(strlen(s)+1);
+	if (p != NULL) {
+		strcpy(p , s);
+	}
+	return p;
+}
-- 
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