SkipStones
Problem Statement 问题描述
When a stone is thrown across water, sometimes it will land on the water and bounce rather than falling in right away. Suppose that a stone is thrown a distance of n. On each successive bounce it will travel half the distance as the previous bounce (rounded down to the nearest integer). When it can not travel any further, it falls into the water. If, at any point, the stone lands on an obstruction rather than water, it will not bounce, but will simply deflect and fall into the water. Please look at the figure for further clarification (with black, red and green cells representing banks, obstructions and free water respectively). So, if the stone is thrown a distance 7, it will bounce and travel a distance of 3, then finally a distance of 1, having travelled a total distance of 11 (the green path in the figure). If a stone is thrown a distance of 8, it will reach the opposite bank, and if thrown at distances of 2 or 6 it will hit an obstruction during its travel. These are the three red paths in the figure.
You are given a String water. An ‘X’ represents an obstruction, while a ‘.’
represents water free from obstruction. You are to return an int representing
the maximum distance a stone can travel and finally fall in the water, without
hitting any obstructions, and without reaching the opposite bank (going beyond
the end of the string). You may choose any initial distance for the throw,
which starts from the left side of the string. A distance of 1 is the first
character of the string, etc. If no initial throw will result in the stone
landing in the water without hitting an obstruction, return 0.
给予一个 String 输入：water. 其内’X'字符代表礁石，’.’ 代表无礁石水面。你的程序
返回一个整数int，表示该石头在最终落入水中的情况下运行的总最大距离，触礁、撞岸的
情形都必须排除。其中撞岸表征为 (字符串访问越上界). 你可以选择任何初始的投掷距离
，出发点为字符串最左侧。距离为1则抵达字符串的第一个字符，依此类推。如果没有投掷
距离，石头被当作直接入水，返回量为0。
定义：
Class:
SkipStones
Method:
maxDistance
Parameters:
String
Returns:
int
Method signature:
int maxDistance(String water)
(确保你的函数为公共类型 public)
注：
礁石处在水面，所以不存在石头入水后撞礁的情形。
限制条件：-
water 字符串包含1到50个元素[即礁石或水面]，1、50包含在内。
water的每个元素包含1到50个字符, 1、50包含在内。
water的每个元素的每个字符要么是’X'，要么是 ‘.’.
测试例子
0)
“..X…..X…”
返回: 11
该例正如题目中（绿色轨迹）所图示。
1)
“…X…”
返回: 3
假如没有该礁石,可以扔一距离4,从而总距离为7。但在有礁石情形下，最佳则是扔出距离2
，再跳1而停止。
2)
“….X….X…XXXX.X…..”
返回: 22
12 + 6 + 3 + 1 = 22, 为最佳结果.
3)
“XXXXXXX.XXX.X..”
返回: 15