PAT-1002 A+B for Polynomials

题目

1002 A+B for Polynomials

题意

给定两个多项式的系数和项,将他们合并

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思路

将系数相同的项累加，累加后若该项为0则删除

误区

1. 项为0的不输出
2. 按照系数大小逆向输出

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源码

#include <iostream>
#include <stdio.h>
#include <map>
using namespace std;
int main()
{
  map<int, double> poly;
  for(int poly_i = 0; poly_i < 2; poly_i++)
  {
      int N;
      cin >> N;

      for(int i = 0; i < N; i++)
      {
          int Ni;
          double aN;
          cin>> Ni >> aN;
          if(poly.find(Ni) != poly.end())
          {
              poly[Ni] += aN;
          }
          else
          {
              poly[Ni] = aN;
          }
          if(poly[Ni] == 0)
          {
              poly.erase(Ni); // 删除项为0
          }

      }
  }
  cout<< poly.size();
  map<int, double>::reverse_iterator rit;
  for(rit = poly.rbegin(); rit != poly.rend(); rit++)
  {
      printf(" %d %.1f", rit->first, rit->second); //保留1位小数
  }
  return 0;
}