Minumum window substring

Signed-off-by: begeekmyfriend <[email protected]>

076_minimum_window_substring/Makefile

@@ -0,0 +1,2 @@
+all:
+	gcc -O2 -o test window_substring.c

076_minimum_window_substring/window_substring.c

@@ -0,0 +1,83 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <limits.h>
+
+static char *minWindow(char *s, char *t)
+{
+    /*
+     * Declare two "hash map" for ASCII chars
+     *   f[]: represents the char found in s
+     *   m[]: stores the chars in t
+     */    
+    int i, f[256], m[256], pat_len = 0;
+    const int NOT_EXISTED   = -1;
+    const int NOT_FOUND     =  0;
+    memset(m, NOT_EXISTED, sizeof(m));
+    memset(f, NOT_EXISTED, sizeof(f));
+
+    /* 
+     *  Go through t, and inital the m[] and f[] 
+     *  Notes: a same char can be appeared multiple times.
+     */
+    for (i = 0; t[i] != '\0'; i++) {
+        m[t[i]] == NOT_EXISTED ? m[t[i]] = 1 : m[t[i]]++; 
+        f[t[i]] = NOT_FOUND;
+        pat_len++;
+    }
+
+    int start =-1;
+    int winSize = INT_MAX;
+    int letterFound = 0;
+    int begin = 0;
+    for (i = 0; s[i] != '\0'; i++) {
+        /* if s[i] is existed in t */ 
+        if (m[s[i]] != NOT_EXISTED){
+            f[s[i]]++;
+
+            /* if one char has been found enough times, then do not do letterFound++ */
+            if (f[s[i]] <= m[s[i]]) {
+                letterFound++;
+            }
+            if (letterFound >= pat_len) {
+                /* 
+                 * Find the beginning of the window
+                 * 1) f[s[begin]] == NOT_EXISTED  ===> the char at the `begin` is not in t
+                 * 2) f[s[begin]] > m[s[begin]]   ===> a same char appeared more than excepted.
+                 */
+                while ( f[s[begin]] == NOT_EXISTED || f[s[begin]] > m[s[begin]] ) { 
+                    if ( f[s[begin]] > m[s[begin]] ) {
+                        f[s[begin]]--;
+                    }   
+                    begin++;
+                }
+                /* Calculate the minimized window size */
+                if(winSize > i - begin + 1){
+                    start = begin;
+                    winSize = i - begin + 1;
+                }     
+            }
+        }
+    }
+
+    char *result = NULL;
+    if (start>=0 && winSize>0) {
+        result = malloc(winSize + 1);
+        memcpy(result, s + start, winSize);
+        result[winSize] = '\0';
+    } else {
+        result = malloc(1);
+        result[0] = '\0';
+    }
+    return result;
+}
+
+int main(int argc, char **argv)
+{
+    if (argc != 3) {
+        fprintf(stderr, "Usage: ./test string pattern\n");
+        exit(-1);
+    }
+    printf("Answer: %s\n", minWindow(argv[1], argv[2]));
+    return 0;
+}