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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.

，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

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)

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 ‘.’.

0)

“..X…..X…”

1)

“…X…”

，再跳1而停止。

2)

“….X….X…XXXX.X…..”

12 + 6 + 3 + 1 = 22, 为最佳结果.

3)

“XXXXXXX.XXX.X..”

posted on 2005-12-13 13:39 emu 阅读(2824) 评论(4)  编辑  收藏 所属分类: google编程大赛模拟题及入围赛真题

### 评论

# re: google中国编程挑战赛资格赛真题 -- SkipStones (朋友转过来的时候顺便给翻译了) 2005-12-13 14:38 Btw0

public class SkipStones {
public int maxDistance(String water) {
int maxDistance = 0;
int lastDistance = 0;
int totalDistance = 0;
for (int i=0; i<water.length(); i++) {
if (water.charAt(i) == 'X') {
maxDistance = 0;
} else {
int distance = (i + 1);
totalDistance = distance;
while (distance/2 >= 1) {
distance = (int)distance/2;
totalDistance += distance;
if ((totalDistance > water.length()) || (water.charAt(totalDistance-1) == 'X')) {
maxDistance = 0;
break;
} else {
maxDistance = totalDistance;
}
}
}
maxDistance = (maxDistance > lastDistance) ? maxDistance : lastDistance;
lastDistance = maxDistance;
}
return maxDistance;
}
public static void main(String[] args){
System.out.println(new SkipStones().maxDistance("..X.....X..."));
System.out.println(new SkipStones().maxDistance("...X..."));
System.out.println(new SkipStones().maxDistance("....X....X...XXXX.X....."));
System.out.println(new SkipStones().maxDistance("XXXXXXX.XXX.X.."));
}
}  回复  更多评论

# re: google中国编程挑战赛资格赛真题 -- SkipStones (朋友转过来的时候顺便给翻译了) 2006-07-30 14:00 eyaswoo

# re: google中国编程挑战赛资格赛真题 -- SkipStones (朋友转过来的时候顺便给翻译了) 2006-07-30 14:01 eyaswoo

# re: google中国编程挑战赛资格赛真题 -- SkipStones (朋友转过来的时候顺便给翻译了) 2008-09-22 16:07 hejian

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