feat: add python and java solutions to lcci question

添加《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

@@ -28,20 +28,41 @@
 
 ## 解法
 <!-- 这里可写通用的实现逻辑 -->
-
+递推法。`f(n)=f(n-1)+f(n-2)+f(n-3)`
 
 ### Python3
 <!-- 这里可写当前语言的特殊实现逻辑 -->
 
 ```python
-
+class Solution:
+    def waysToStep(self, n: int) -> int:
+        if n < 3:
+            return n
+        a, b, c = 1, 2, 4
+        for i in range(4, n + 1):
+            a, b, c = b, c, (a + b + c) % 1000000007
+        return c
 ```
 
 ### Java
 <!-- 这里可写当前语言的特殊实现逻辑 -->
 
 ```java
-
+class Solution {
+    public int waysToStep(int n) {
+        if (n < 3) {
+            return n;
+        }
+        int a = 1, b = 2, c = 4;
+        for (int i = 4; i <= n; ++i) {
+            int t = a;
+            a = b;
+            b = c;
+            c = ((a + b) % 1000000007 + t) % 1000000007;
+        }
+        return c;
+    }
+}
 ```
 
 ### ...

lcci/08.01.Three Steps Problem/README_EN.md

@@ -1,46 +1,79 @@
-# [08.01. Three Steps Problem](https://leetcode-cn.com/problems/three-steps-problem-lcci)
-
-## Description
-<p>A child is running up a staircase with n steps and can hop either 1 step, 2 steps, or 3 steps at a time. Implement a method to count how many possible ways the child can run up the stairs.&nbsp;The result may be large, so return it modulo 1000000007.</p>
-
-<p><strong>Example1:</strong></p>
-
-<pre>
-<strong> Input</strong>: n = 3 
-<strong> Output</strong>: 4
-</pre>
-
-<p><strong>Example2:</strong></p>
-
-<pre>
-<strong> Input</strong>: n = 5
-<strong> Output</strong>: 13
-</pre>
-
-<p><strong>Note:</strong></p>
-
-<ol>
-	<li><code>1 &lt;= n &lt;= 1000000</code></li>
-</ol>
-
-
-
-## Solutions
-
-
-### Python3
-
-```python
-
-```
-
-### Java
-
-```java
-
-```
-
-### ...
-```
-
-```
+# [08.01. Three Steps Problem](https://leetcode-cn.com/problems/three-steps-problem-lcci)
+
+## Description
+<p>A child is running up a staircase with n steps and can hop either 1 step, 2 steps, or 3 steps at a time. Implement a method to count how many possible ways the child can run up the stairs.&nbsp;The result may be large, so return it modulo 1000000007.</p>
+
+
+
+<p><strong>Example1:</strong></p>
+
+
+
+<pre>
+
+<strong> Input</strong>: n = 3 
+
+<strong> Output</strong>: 4
+
+</pre>
+
+
+
+<p><strong>Example2:</strong></p>
+
+
+
+<pre>
+
+<strong> Input</strong>: n = 5
+
+<strong> Output</strong>: 13
+
+</pre>
+
+
+
+<p><strong>Note:</strong></p>
+
+1. `1 <= n <= 1000000`
+
+## Solutions
+
+
+### Python3
+
+```python
+class Solution:
+    def waysToStep(self, n: int) -> int:
+        if n < 3:
+            return n
+        a, b, c = 1, 2, 4
+        for i in range(4, n + 1):
+            a, b, c = b, c, (a + b + c) % 1000000007
+        return c
+```
+
+### Java
+
+```java
+class Solution {
+    public int waysToStep(int n) {
+        if (n < 3) {
+            return n;
+        }
+        int a = 1, b = 2, c = 4;
+        for (int i = 4; i <= n; ++i) {
+            int t = a;
+            a = b;
+            b = c;
+            c = ((a + b) % 1000000007 + t) % 1000000007;
+        }
+        return c;
+    }
+}
+```
+
+### ...
+```
+
+```

lcci/08.01.Three Steps Problem/Solution.java

@@ -0,0 +1,15 @@
+class Solution {
+    public int waysToStep(int n) {
+        if (n < 3) {
+            return n;
+        }
+        int a = 1, b = 2, c = 4;
+        for (int i = 4; i <= n; ++i) {
+            int t = a;
+            a = b;
+            b = c;
+            c = ((a + b) % 1000000007 + t) % 1000000007;
+        }
+        return c;
+    }
+}

lcci/08.01.Three Steps Problem/Solution.py

@@ -0,0 +1,8 @@
+class Solution:
+    def waysToStep(self, n: int) -> int:
+        if n < 3:
+            return n
+        a, b, c = 1, 2, 4
+        for i in range(4, n + 1):
+            a, b, c = b, c, (a + b + c) % 1000000007
+        return c