POJ 2418 Hardwood Species （map）

题目通道：POJ 2418

第一次用map，中间费了点周折，string类的输入输出一直存在问题，string类不能scanf直接输入，要提前预订大小，string a; a.resize(100); scanf("%s",&a[0]); 如果多个字符串输入，用getline(cin, s)即可，空格也能读入

Describe:

Hardwoods are the botanical group of trees that have broad leaves, produce a fruit or nut, and generally go dormant in the winter.
America's temperate climates produce forests with hundreds of hardwood species -- trees that share certain biological characteristics. Although oak, maple and cherry all are types of hardwood trees, for example, they are different species. Together, all the hardwood species represent 40 percent of the trees in the United States.

On the other hand, softwoods, or conifers, from the Latin word meaning "cone-bearing," have needles. Widely available US softwoods include cedar, fir, hemlock, pine, redwood, spruce and cypress. In a home, the softwoods are used primarily as structural lumber such as 2x4s and 2x6s, with some limited decorative applications.

Using satellite imaging technology, the Department of Natural Resources has compiled an inventory of every tree standing on a particular day. You are to compute the total fraction of the tree population represented by each species.

Input:

Input to your program consists of a list of the species of every tree observed by the satellite; one tree per line. No species name exceeds 30 characters. There are no more than 10,000 species and no more than 1,000,000 trees.

Output:

Print the name of each species represented in the population, in alphabetical order, followed by the percentage of the population it represents, to 4 decimal places.

Sample Input:

Red Alder
Ash
Aspen
Basswood
Ash
Beech
Yellow Birch
Ash
Cherry
Cottonwood
Ash
Cypress
Red Elm
Gum
Hackberry
White Oak
Hickory
Pecan
Hard Maple
White Oak
Soft Maple
Red Oak
Red Oak
White Oak
Poplan
Sassafras
Sycamore
Black Walnut
Willow

Sample Output:

Ash 13.7931
Aspen 3.4483
Basswood 3.4483
Beech 3.4483
Black Walnut 3.4483
Cherry 3.4483
Cottonwood 3.4483
Cypress 3.4483
Gum 3.4483
Hackberry 3.4483
Hard Maple 3.4483
Hickory 3.4483
Pecan 3.4483
Poplan 3.4483
Red Alder 3.4483
Red Elm 3.4483
Red Oak 6.8966
Sassafras 3.4483
Soft Maple 3.4483
Sycamore 3.4483
White Oak 10.3448
Willow 3.4483
Yellow Birch 3.4483

题目大意：

给一堆树的名字，问每种树的个数占比多少，按字典序输出，保留四位小数。

题目思路：

思路是没难度，用map做就是记录每个树个数，最后算一下就行，主要是map的一些操作熟练一下，printf不能直接输出string类，得用string.c_str()函数编程字符数组再输出。

AC代码：

 

#include <iostream>
#include <cstdio>
#include <map>
#include <string>
using namespace std;
int main()
{
    map<string, double> m; // 建立map
    map<string, double>::iterator iter; // 创建迭代器类型
    string s;
    int n = 0; // 计数器
    while(getline(cin,s)) // 可以读入空格，学到了
    {
        m[s]++;
        n++;
    }
    for(iter=m.begin(); iter!=m.end(); iter++) // 遍历map，输出
    {
        printf("%s %.4f\n",(iter->first).c_str(),(iter->second)*100.0/n);
    }
    return 0;
}