coursera scala week one

http://blog.csdn.net/unhappypeople/article/details/17199951

1. 杨辉三角

   • 边界1
   • 其他是上一行的两个数的和

  def pascal(c:Int,r:Int): Int ={if (c == 0 || c == r|| r==0) 1else pascal(c-1,r-1) + pascal(c,r-1)}

1. 括号平衡
   
   • 遇到左括号+1
   • 遇到右括号-1
   • count小于零false，chars为空且count为0 true

def balance(chars: String): Boolean ={def isMatch(chars: String,count:Int):Boolean={if (count < 0) falseelse if(chars.isEmpty) count == 0else if(chars.head == '('){isMatch(chars.tail,count+1)}else if (chars.head == ')'){isMatch(chars.tail,count -1)}else{isMatch(chars.tail,count)}}isMatch(chars,0)
}
println(balance("()()!"))

1. 硬币组合
   
   • 假设有三个硬币ABC，只考虑A，
     1.不用A 2.用一次A 3.用多次A

def count(vs: List[Int],all:Int):Int={if (all == 0) 1else if(vs.isEmpty) 0else if(all < 0) 0elsecount(vs.tail,all)+ count(vs,all-vs.head)
}