feat: leetcode/91

src/leetcode/algorithm_91/README.md

@@ -0,0 +1,3 @@
+Decode Ways
+===========
+[leetcode](https://leetcode.com/problems/decode-ways/)

src/leetcode/algorithm_91/first.rs

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+pub struct Solution;
+
+impl Solution {
+    pub fn num_decodings(s: String) -> i32 {
+        if s.is_empty() {
+            return 0;
+        }
+        let mut previous = 1;
+        let mut ways = 1;
+        let digits = s.into_bytes();
+        let mut digits = digits.iter().map(|c| c - 0x30);
+        let mut last = digits.next().unwrap();
+        if last == 0 {
+            return 0;
+        }
+        for d in digits {
+            if d == 0 {
+                if last > 0 && last <= 2 {
+                    ways = previous;
+                } else {
+                    return 0;
+                }
+            } else {
+                let temp = ways;
+                if last > 0 && last * 10 + d <= 26 {
+                    ways += previous;
+                }
+                previous = temp;
+            }
+            last = d;
+        }
+        ways
+    }
+}

src/leetcode/algorithm_91/mod.rs

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+pub mod first;
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use test_case::test_case;
+
+    #[test_case("12" => 2; "example 1")]
+    #[test_case("06" => 0; "case 1")]
+    #[test_case("0" => 0; "case 2")]
+    #[test_case("10" => 1; "case 3")]
+    #[test_case("2101" => 1; "case 4")]
+    #[test_case("1123" => 5; "case 5")]
+    #[test_case("112" => 3; "case 6")]
+    #[test_case("123123" => 9; "case 7")]
+    #[test_case("2611055971756562" => 4; "case 8")]
+    #[test_case("26110" => 2; "case 9")]
+    #[test_case("2611" => 4; "case 10")]
+    #[test_case("12120" => 3; "case 11")]
+    fn test_first_solution(s: &str) -> i32 {
+        first::Solution::num_decodings(s.to_string())
+    }
+}

src/leetcode/mod.rs

@@ -1,3 +1,4 @@
+pub mod algorithm_91;
 pub mod algorithm_76;
 pub mod algorithm_79;
 pub mod algorithm_73;