feat: add rust solution to lcci problem: No.08.01

No.08.01.Three Steps Problem

Author: YangFong

lcci/08.01.Three Steps Problem/README.md

@@ -92,6 +92,27 @@ var waysToStep = function (n) {
 };
 ```
 
+### **C**
+
+```c
+int waysToStep(int n)
+{
+    if (n < 3)
+    {
+        return n;
+    }
+    int a = 1, b = 2, c = 4, i = 4;
+    while (i++ <= n)
+    {
+        int t = ((a + b) % 1000000007 + c) % 1000000007;
+        a = b;
+        b = c;
+        c = t;
+    }
+    return c;
+}
+```
+
 ### **C++**
 
 ```cpp
@@ -113,4 +134,26 @@ public:
 };
 ```
 
+### **Rust**
+
+```rust
+impl Solution {
+    pub fn ways_to_step(n: i32) -> i32 {
+        let mut dp = [1, 2, 4];
+        let n = n as usize;
+        if n <= 3 {
+            return dp[n - 1];
+        }
+        for _ in 3..n {
+            dp = [
+                dp[1],
+                dp[2],
+                (((dp[0] + dp[1]) % 1000000007) + dp[2]) % 1000000007,
+            ];
+        }
+        dp[2]
+    }
+}
+```
+
 <!-- tabs:end -->

lcci/08.01.Three Steps Problem/README_EN.md

@@ -86,6 +86,27 @@ var waysToStep = function (n) {
 };
 ```
 
+### **C**
+
+```c
+int waysToStep(int n)
+{
+    if (n < 3)
+    {
+        return n;
+    }
+    int a = 1, b = 2, c = 4, i = 4;
+    while (i++ <= n)
+    {
+        int t = ((a + b) % 1000000007 + c) % 1000000007;
+        a = b;
+        b = c;
+        c = t;
+    }
+    return c;
+}
+```
+
 ### **C++**
 
 ```cpp
@@ -107,4 +128,26 @@ public:
 };
 ```
 
+### **Rust**
+
+```rust
+impl Solution {
+    pub fn ways_to_step(n: i32) -> i32 {
+        let mut dp = [1, 2, 4];
+        let n = n as usize;
+        if n <= 3 {
+            return dp[n - 1];
+        }
+        for _ in 3..n {
+            dp = [
+                dp[1],
+                dp[2],
+                (((dp[0] + dp[1]) % 1000000007) + dp[2]) % 1000000007,
+            ];
+        }
+        dp[2]
+    }
+}
+```
+
 <!-- tabs:end -->

lcci/08.01.Three Steps Problem/Solution.rs

@@ -0,0 +1,17 @@
+impl Solution {
+    pub fn ways_to_step(n: i32) -> i32 {
+        let mut dp = [1, 2, 4];
+        let n = n as usize;
+        if n <= 3 {
+            return dp[n - 1];
+        }
+        for _ in 3..n {
+            dp = [
+                dp[1],
+                dp[2],
+                (((dp[0] + dp[1]) % 1000000007) + dp[2]) % 1000000007,
+            ];
+        }
+        dp[2]
+    }
+}