1915. Number of Wonderful Substrings: AC

Author: tan-wei

src/solution/mod.rs

@@ -1444,3 +1444,4 @@ mod s1911_maximum_alternating_subsequence_sum;
 mod s1912_design_movie_rental_system;
 mod s1913_maximum_product_difference_between_two_pairs;
 mod s1914_cyclically_rotating_a_grid;
+mod s1915_number_of_wonderful_substrings;

src/solution/s1915_number_of_wonderful_substrings.rs

@@ -0,0 +1,122 @@
+/**
+ * [1915] Number of Wonderful Substrings
+ *
+ * A wonderful string is a string where at most one letter appears an odd number of times.
+ *
+ *
+ * 	For example, "ccjjc" and "abab" are wonderful, but "ab" is not.
+ *
+ *
+ * Given a string word that consists of the first ten lowercase English letters ('a' through 'j'), return the number of wonderful non-empty substrings in word. If the same substring appears multiple times in word, then count each occurrence separately.
+ *
+ * A substring is a contiguous sequence of characters in a string.
+ *
+ *  
+ * Example 1:
+ *
+ *
+ * Input: word = "aba"
+ * Output: 4
+ * Explanation: The four wonderful substrings are underlined below:
+ * - "<u>a</u>ba" -> "a"
+ * - "a<u>b</u>a" -> "b"
+ * - "ab<u>a</u>" -> "a"
+ * - "<u>aba</u>" -> "aba"
+ *
+ *
+ * Example 2:
+ *
+ *
+ * Input: word = "aabb"
+ * Output: 9
+ * Explanation: The nine wonderful substrings are underlined below:
+ * - "<u>a</u>abb" -> "a"
+ * - "<u>aa</u>bb" -> "aa"
+ * - "<u>aab</u>b" -> "aab"
+ * - "<u>aabb</u>" -> "aabb"
+ * - "a<u>a</u>bb" -> "a"
+ * - "a<u>abb</u>" -> "abb"
+ * - "aa<u>b</u>b" -> "b"
+ * - "aa<u>bb</u>" -> "bb"
+ * - "aab<u>b</u>" -> "b"
+ *
+ *
+ * Example 3:
+ *
+ *
+ * Input: word = "he"
+ * Output: 2
+ * Explanation: The two wonderful substrings are underlined below:
+ * - "<u>h</u>e" -> "h"
+ * - "h<u>e</u>" -> "e"
+ *
+ *
+ *  
+ * Constraints:
+ *
+ *
+ * 	1 <= word.length <= 10^5
+ * 	word consists of lowercase English letters from 'a' to 'j'.
+ *
+ */
+pub struct Solution {}
+
+// problem: https://leetcode.com/problems/number-of-wonderful-substrings/
+// discuss: https://leetcode.com/problems/number-of-wonderful-substrings/discuss/?currentPage=1&orderBy=most_votes&query=
+
+// submission codes start here
+
+impl Solution {
+    pub fn wonderful_substrings(word: String) -> i64 {
+        word.bytes()
+            .fold(
+                (0usize, 0i64, {
+                    let mut v = vec![0i64; 1024];
+                    v[0] = 1;
+                    v
+                }),
+                |(mut x, mut ans, mut v), c| {
+                    x ^= 1 << (c - 97);
+                    ans += v[x];
+                    ans += (0..10).map(|i| v[x ^ (1 << i)]).sum::<i64>();
+                    v[x] += 1;
+                    (x, ans, v)
+                },
+            )
+            .1
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_1915_example_1() {
+        let word = "aba".to_string();
+
+        let result = 4;
+
+        assert_eq!(Solution::wonderful_substrings(word), result);
+    }
+
+    #[test]
+    fn test_1915_example_2() {
+        let word = "aabb".to_string();
+
+        let result = 9;
+
+        assert_eq!(Solution::wonderful_substrings(word), result);
+    }
+
+    #[test]
+    fn test_1915_example_3() {
+        let word = "he".to_string();
+
+        let result = 2;
+
+        assert_eq!(Solution::wonderful_substrings(word), result);
+    }
+}