Merge pull request neetcode-gh#2220 from seinlin/438

Add 0438-find-all-anagrams-in-a-string.c

Author: MHamiid

c/0438-find-all-anagrams-in-a-string.c

@@ -0,0 +1,47 @@
+#define TO_INDEX(c) c - 'a'
+
+bool isEquals(int* a, int* b, int n) {
+    for (int i = 0; i < n; i++) {
+        if (a[i] != b[i]) {
+            return false;
+        }
+    }
+    return true;
+}
+
+/**
+ * Note: The returned array must be malloced, assume caller calls free().
+ */
+int* findAnagrams(char * s, char * p, int* returnSize) {
+    int sSize = strlen(s);
+    int pSize = strlen(p);
+    int pFreq[26] = {0};
+    int sFreq[26] = {0};
+    int i, count;
+    int* ans;
+
+    if (sSize < pSize) {
+        *returnSize = 0;
+        return ans;
+    }
+
+    for (i = 0; i < pSize; i++) {
+        pFreq[TO_INDEX(p[i])]++;
+        sFreq[TO_INDEX(s[i])]++;
+    }
+
+    count = 0;
+    ans = (int*)calloc(sSize - pSize + 1, sizeof(int));
+    for (i = 0; i <= sSize - pSize; i++) {
+        if (i > 0) {
+            sFreq[TO_INDEX(s[i - 1])]--;
+            sFreq[TO_INDEX(s[i + pSize - 1])]++;
+        }
+        if (isEquals(sFreq, pFreq, 26)) {
+            ans[count++] = i;
+        }
+    }
+    *returnSize = count;
+
+    return ans;
+}