feat: update solutions to lcci question:08.01.Three Steps Problem

更新《程序员面试金典》题解：面试题 08.01. 三步问题

Author: yanglbme

lcci/08.01.Three Steps Problem/README.md

@@ -39,7 +39,7 @@ class Solution:
         if n < 3:
             return n
         a, b, c = 1, 2, 4
-        for i in range(4, n + 1):
+        for _ in range(4, n + 1):
             a, b, c = b, c, (a + b + c) % 1000000007
         return c
 ```
@@ -65,7 +65,22 @@ class Solution {
 }
 ```
 
-### ...
-```
-
+### C++
+```cpp
+class Solution {
+public:
+    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;
+    }
+};
 ```

lcci/08.01.Three Steps Problem/README_EN.md

@@ -48,7 +48,7 @@ class Solution:
         if n < 3:
             return n
         a, b, c = 1, 2, 4
-        for i in range(4, n + 1):
+        for _ in range(4, n + 1):
             a, b, c = b, c, (a + b + c) % 1000000007
         return c
 ```
@@ -73,7 +73,22 @@ class Solution {
 }
 ```
 
-### ...
-```
-
+### C++
+```cpp
+class Solution {
+public:
+    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;
+    }
+};
 ```

lcci/08.01.Three Steps Problem/Solution.c

@@ -0,0 +1,16 @@
+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;
+}

lcci/08.01.Three Steps Problem/Solution.cpp

@@ -0,0 +1,16 @@
+class Solution {
+public:
+    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;
+    }
+};

lcci/08.01.Three Steps Problem/Solution.py

@@ -3,6 +3,6 @@ def waysToStep(self, n: int) -> int:
         if n < 3:
             return n
         a, b, c = 1, 2, 4
-        for i in range(4, n + 1):
+        for _ in range(4, n + 1):
             a, b, c = b, c, (a + b + c) % 1000000007
         return c