Merge pull request #1484 from wzqwtt/dp01

添加（0509.斐波那契数、0070.爬楼梯、0746.使用最小花费爬楼梯） Scala版本

problems/0070.爬楼梯.md

@@ -401,6 +401,38 @@ int climbStairs(int n){
 }
 ```
 
+### Scala
+
+```scala
+object Solution {
+  def climbStairs(n: Int): Int = {
+    if (n <= 2) return n
+    var dp = new Array[Int](n + 1)
+    dp(1) = 1
+    dp(2) = 2
+    for (i <- 3 to n) {
+      dp(i) = dp(i - 1) + dp(i - 2)
+    }
+    dp(n)
+  }
+}
+```
+
+优化空间复杂度:
+```scala
+object Solution {
+  def climbStairs(n: Int): Int = {
+    if (n <= 2) return n
+    var (a, b) = (1, 2)
+    for (i <- 3 to n) {
+      var tmp = a + b
+      a = b
+      b = tmp
+    }
+    b // 最终返回b
+  }
+}
+```
 
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 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>

problems/0509.斐波那契数.md

@@ -263,7 +263,7 @@ var fib = function(n) {
 };
 ```
 
-TypeScript
+### TypeScript
 
 ```typescript
 function fib(n: number): number {
@@ -342,5 +342,33 @@ pub fn fib(n: i32) -> i32 {
     return fib(n - 1) + fib(n - 2);
 }
 ```
+
+### Scala
+
+动态规划:
+```scala
+object Solution {
+  def fib(n: Int): Int = {
+    if (n <= 1) return n
+    var dp = new Array[Int](n + 1)
+    dp(1) = 1
+    for (i <- 2 to n) {
+      dp(i) = dp(i - 1) + dp(i - 2)
+    }
+    dp(n)
+  }
+}
+```
+
+递归:
+```scala
+object Solution {
+  def fib(n: Int): Int = {
+    if (n <= 1) return n
+    fib(n - 1) + fib(n - 2)
+  }
+}
+```
+
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 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>

problems/0746.使用最小花费爬楼梯.md

@@ -323,5 +323,35 @@ int minCostClimbingStairs(int* cost, int costSize){
     return dp[i-1] < dp[i-2] ? dp[i-1] : dp[i-2];
 }
 ```
+
+### Scala
+
+```scala
+object Solution {
+  def minCostClimbingStairs(cost: Array[Int]): Int = {
+    var dp = new Array[Int](cost.length)
+    dp(0) = cost(0)
+    dp(1) = cost(1)
+    for (i <- 2 until cost.length) {
+      dp(i) = math.min(dp(i - 1), dp(i - 2)) + cost(i)
+    }
+    math.min(dp(cost.length - 1), dp(cost.length - 2))
+  }
+}
+```
+
+第二种思路: dp[i] 表示爬到第i-1层所需的最小花费，状态转移方程为: dp[i] = min(dp[i-1]+cost[i-1],dp[i-2]+cost[i-2])
+```scala
+object Solution {
+  def minCostClimbingStairs(cost: Array[Int]): Int = {
+    var dp = new Array[Int](cost.length + 1)
+    for (i <- 2 until cost.length + 1) {
+      dp(i) = math.min(dp(i - 1) + cost(i - 1), dp(i - 2) + cost(i - 2))
+    }
+    dp(cost.length)
+  }
+}
+```
+
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 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>