[POJ] #1005# I Think I Need a Houseboat : 浮点数运算

一. 题目

I Think I Need a Houseboat

Time Limit: 1000MS		Memory Limit: 10000K
Total Submissions: 97512		Accepted: 42430

Description

Fred Mapper is considering purchasing some land in Louisiana to build his house on. In the process of investigating the land, he learned that the state of Louisiana is actually shrinking by 50 square miles each year, due to erosion caused by the Mississippi River. Since Fred is hoping to live in this house the rest of his life, he needs to know if his land is going to be lost to erosion.

After doing more research, Fred has learned that the land that is
being lost forms a semicircle. This semicircle is part of a circle
centered at (0,0), with the line that bisects the circle being the X
axis. Locations below the X axis are in the water. The semicircle has an
area of 0 at the beginning of year 1. (Semicircle illustrated in the
Figure.)

Input

The
first line of input will be a positive integer indicating how many data
sets will be included (N). Each of the next N lines will contain the X
and Y Cartesian coordinates of the land Fred is considering. These will
be floating point numbers measured in miles. The Y coordinate will be
non-negative. (0,0) will not be given.

Output

For
each data set, a single line of output should appear. This line should
take the form of: “Property N: This property will begin eroding in year
Z.” Where N is the data set (counting from 1), and Z is the first year
(start from 1) this property will be within the semicircle AT THE END OF
YEAR Z. Z must be an integer. After the last data set, this should
print out “END OF OUTPUT.”

Sample Input

2
1.0 1.0
25.0 0.0

Sample Output

Property 1: This property will begin eroding in year 1.
Property 2: This property will begin eroding in year 20.
END OF OUTPUT.

Hint

1.No property will appear exactly on the semicircle boundary: it will either be inside or outside.
2.This problem will be judged automatically. Your answer must match
exactly, including the capitalization, punctuation, and white-space.
This includes the periods at the ends of the lines.

3.All locations are given in miles.

Source

Mid-Atlantic 2001

二. 题意

• 河水以每年50平方为单位，呈半圆形扩张侵蚀土地
• 以半圆中心点（0, 0）, 建立坐标系
• 给出坐标(x, y)，输出该点土地在哪一年会被侵蚀

三. 分析

• 算法核心: 题目较为简单，只需知道基本的求圆面积的几何公式
• 实现细节:
  • 圆面积公式
  • 结果输出的条件判断
  • 浮点类型运算

四. 题解

 #include <stdio.h>
 #define PI 3.1415927

 int main()
 {
     int area, year, i, count;
     float x, y;

     scanf("%d\n", &count);
     for (i = ; i <= count; i++) {
         scanf("%f %f\n", &x, &y);

         area = ; year = ;
         while () {
             area += ;
             if (area > (PI * (x * x + y * y) / )) break;
             year++;
         }
         printf("Property %d: This property will begin eroding in year %ld.\n", i, year);
     }

     printf("END OF OUTPUT.\n");
     return ;
 }