Merge pull request #1861 from tahsintunan/438

Update 438. Find All Anagrams in a String with more performant code

Author: tahsintunan

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

@@ -1,38 +1,31 @@
 func findAnagrams(s string, p string) []int {
-    startIndex := 0
-    pMap := make(map[byte]int)
-    sMap := make(map[byte]int)
-    var res []int
-    
-    for i := 0; i < len(p); i++ {
-        pMap[p[i]] = 1 + pMap[p[i]]
-    }
-    
-    for i := 0; i < len(s); i++ {
-        sMap[s[i]] = 1 + sMap[s[i]]
-        
-        if i >= len(p) - 1 {
-            if equals(sMap, pMap) {
-                res = append(res, startIndex)
-            }
-            
-            if _, ok := sMap[s[startIndex]]; ok {
-                sMap[s[startIndex]] = sMap[s[startIndex]] - 1
-                if sMap[s[startIndex]] == 0 {
-                    delete(sMap, s[startIndex])
-                }
-            }
-            startIndex += 1
-        }
-    }
-    return res
-}
+	len_s, len_p := len(s), len(p)
+	if len_p > len_s {
+		return []int{}
+	}
+
+	ans := make([]int, 0, len_s)
+	count_p, count_s := count(p), count(s[:len_p])
+
+	if count_p == count_s {
+		ans = append(ans, 0)
+	}
 
-func equals(a, b map[byte]int) bool {
-    for k, v := range a {
-        if b[k] != v {
-            return false
-        }
-    }
-    return true
+	for i := len_p; i < len_s; i++ {
+		count_s[int(s[i-len_p]-'a')]--
+		count_s[int(s[i]-'a')]++
+		if count_p == count_s {
+			ans = append(ans, i-len_p+1)
+		}
+	}
+
+	return ans
 }
+
+func count(s string) [26]int {
+	arr := [26]int{}
+	for _, r := range []rune(s) {
+		arr[int(r-'a')]++
+	}
+	return arr
+}