0070. Climbing Stairs

Author: coderbean

markdown/0070. Climbing Stairs.md

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+### [70\. Climbing Stairs](https://leetcode.com/problems/climbing-stairs/)
+
+Difficulty: **Easy**
+
+
+You are climbing a stair case. It takes _n_ steps to reach to the top.
+
+Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?
+
+**Note:** Given _n_ will be a positive integer.
+
+**Example 1:**
+
+```
+Input: 2
+Output: 2
+Explanation: There are two ways to climb to the top.
+1\. 1 step + 1 step
+2\. 2 steps
+```
+
+**Example 2:**
+
+```
+Input: 3
+Output: 3
+Explanation: There are three ways to climb to the top.
+1\. 1 step + 1 step + 1 step
+2\. 1 step + 2 steps
+3\. 2 steps + 1 step
+```
+
+
+#### Solution
+
+Language: **Java**
+
+```java
+class Solution {
+    public int climbStairs(int n) {
+        int[] dp = new int[n + 1];
+        return this.climbStairs(dp, n);
+​
+    }
+​
+    private int climbStairs(int[] dp, int n) {
+        if (n <= 1) {
+            return 1;
+        }
+        if (dp[n] > 0) {
+            return dp[n];
+        }
+        int num = climbStairs(dp, n - 1) + climbStairs(dp, n - 2);
+        dp[n] = num;
+        return num;
+    }
+}
+```
+![](https://raw.githubusercontent.com/PicGoBed/PicBed/master/20190720171004.png)

src/main/java/leetcode/_70_/Main.java

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+package leetcode._70_;
+
+/**
+ * Created by zhangbo54 on 2019-03-04.
+ */
+public class Main {
+    public static void main(String[] args) {
+        Solution solution = new Solution();
+        System.out.println( solution.climbStairs(0));
+        System.out.println( solution.climbStairs(2));
+        System.out.println( solution.climbStairs(3));
+        System.out.println( solution.climbStairs(1));
+        System.out.println( solution.climbStairs(111));
+    }
+}
+

src/main/java/leetcode/_70_/Solution.java

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+package leetcode._70_;
+
+class Solution {
+    public int climbStairs(int n) {
+        int[] dp = new int[n + 1];
+        return this.climbStairs(dp, n);
+
+    }
+
+    private int climbStairs(int[] dp, int n) {
+        if (n <= 1) {
+            return 1;
+        }
+        if (dp[n] > 0) {
+            return dp[n];
+        }
+        int num = climbStairs(dp, n - 1) + climbStairs(dp, n - 2);
+        dp[n] = num;
+        return num;
+    }
+}

src/main/java/leetcode/_70_/solution.md

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+### [70\. Climbing Stairs](https://leetcode.com/problems/climbing-stairs/)
+
+Difficulty: **Easy**
+
+
+You are climbing a stair case. It takes _n_ steps to reach to the top.
+
+Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?
+
+**Note:** Given _n_ will be a positive integer.
+
+**Example 1:**
+
+```
+Input: 2
+Output: 2
+Explanation: There are two ways to climb to the top.
+1\. 1 step + 1 step
+2\. 2 steps
+```
+
+**Example 2:**
+
+```
+Input: 3
+Output: 3
+Explanation: There are three ways to climb to the top.
+1\. 1 step + 1 step + 1 step
+2\. 1 step + 2 steps
+3\. 2 steps + 1 step
+```
+
+
+#### Solution
+
+Language: **Java**
+
+```java
+class Solution {
+    public int climbStairs(int n) {
+        int[] dp = new int[n + 1];
+        return this.climbStairs(dp, n);
+​
+    }
+​
+    private int climbStairs(int[] dp, int n) {
+        if (n <= 1) {
+            return 1;
+        }
+        if (dp[n] > 0) {
+            return dp[n];
+        }
+        int num = climbStairs(dp, n - 1) + climbStairs(dp, n - 2);
+        dp[n] = num;
+        return num;
+    }
+}
+```
+![](https://raw.githubusercontent.com/PicGoBed/PicBed/master/20190720171004.png)