Merge pull request haoel#98 from xusiwei/master

C solution for "Reverse Words in a String", in O(1) space

Author: haoel

algorithms/cpp/reverseWordsInAString/reverseWordsInAString.cpp

@@ -24,9 +24,13 @@
 **********************************************************************************/
 
 #include <ctype.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
 #include <iostream>
 #include <string>
 #include <vector>
+#include <algorithm>  // for std::reverse
 using namespace std;
 
 void reverseWords(string &s) {
@@ -100,6 +104,53 @@ void reverseWords2(string &s) {
     s.swap(result);
 }
 
+
+// C solution in O(1) space
+void reverse(char *b, char *e) {
+    for (--e; e - b > 0; b++, e--) {
+        char t = *b;
+        *b = *e;
+        *e = t;
+    }
+}
+
+void reverseWords(char *s) {
+    char *p = s, *ws = NULL, *last = s;
+
+    while (*p && *p == ' ') p++; // skip leading space
+    ws = p;
+
+    for ( ; *p; p++) {
+        while (*p && *p != ' ') p++; // find word end
+
+        reverse(ws, p);
+        strncpy(last, ws, p-ws);
+        last += (p-ws);
+
+        while (*p && *p == ' ') p++; // for next word
+        ws = p;
+
+        if (*p == '\0') break;
+        *last++ = ' ';
+    }
+    reverse(s, last);
+    *last = '\0';
+}
+
+void test() {
+#define TEST(str) do {       \
+    char* s = strdup(str);   \
+    printf("\"%s\" => ", s); \
+    reverseWords(s);         \
+    printf("\"%s\"\n\n", s); \
+    free(s);                 \
+    } while (0)
+
+    TEST("  the    blue   sky  is blue    ");
+    TEST("  ");
+}
+
+
 main()
 {
    string s;
@@ -113,4 +164,5 @@ main()
    s="i love cpp";
    reverseWords(s);
 
+   test();
 }