Add substring_anagrams

Author: marttp

rust/Sliding Windows/substring_anagrams.rs

@@ -0,0 +1,35 @@
+fn substring_anagrams(s: String, t: String) -> i32 {
+    let len_s = s.len();
+    let len_t = t.len();
+    if len_t > len_s {
+        return 0;
+    }
+    let mut count = 0;
+    let mut expected_freqs = vec![0; 26];
+    let mut window_freqs = vec![0; 26];
+    // Populate 'expected_freqs' with the characters in string 't'.
+    for c in t.bytes() {
+        expected_freqs[(c - b'a') as usize] += 1;
+    }
+    let mut left = 0;
+    let mut right = 0;
+    while right < len_s {
+        // Add the character at the right pointer to 'window_freqs'
+        // before sliding the window.
+        window_freqs[(s.as_bytes()[right] - b'a') as usize] += 1;
+        // If the window has reached the expected fixed length, we
+        // advance the left pointer as well as the right pointer to
+        // slide the window.
+        if right - left + 1 == len_t {
+            if window_freqs == expected_freqs {
+                count += 1;
+            }
+            // Remove the character at the left pointer from
+            // 'window_freqs' before advancing the left pointer.
+            window_freqs[(s.as_bytes()[left] - b'a') as usize] -= 1;
+            left += 1;
+        }
+        right += 1;
+    }
+    count
+}