算法进阶指南-基础算法-贪心

1.Sunscreen
题目链接

代码:

import java.util.Arrays;
import java.util.Comparator;
import java.util.Scanner;
import java.util.HashMap;
public class Main {
    public static void main(String[] args) {
         Scanner in = new Scanner(System.in);
         int C = in.nextInt();
         int L = in.nextInt();
         int[] minSPF = new int[C];
         int[] maxSPF = new int[C];
         int[] SPF = new int[L];
         int[] cover = new int[L];
         for(int i=0;i<C;i++){
             minSPF[i]=in.nextInt();
             maxSPF[i]=in.nextInt();
         }
         for(int i=0;i<L;i++){
             SPF[i]=in.nextInt();
             cover[i]=in.nextInt();
         }
         Integer[] c = new Integer[C];
         for(int i=0;i<C;i++)c[i]=i;
         Arrays.sort(c, new Comparator<Integer>() {
             @Override
             public int compare(Integer o1, Integer o2) {
                 return minSPF[o2]-minSPF[o1];
             }
         });
         int res = 0;
         for(int i=0;i<C;i++){
             int ix = c[i];
             int minSPFi = minSPF[ix];
             int maxSPFi = maxSPF[ix];
             int maxIx = 0;
             int maxSPFC = Integer.MIN_VALUE;
             boolean findOne = false;
             for(int j=0;j<L;j++){
                 if(SPF[j]>=minSPFi&&SPF[j]<=maxSPFi){
                     //需要满足条件
                     //System.out.println("im in!");
                     if(SPF[j]>maxSPFC&&cover[j]>0){
                         maxSPFC=SPF[j];
                         maxIx = j;
                         findOne=true;
                         //System.out.println(maxIx);
                     }
                 }
             }
             /*
             贪心策略：由于minSPF按照递减策略排序，那么每一个不低于当前minSPF的防晒霜都不会低于其他后续防晒霜的minSPF，
             对于当前可选的x，y，如果SPF[y]>SFP[x],那么后续奶牛只可能有三种情况“x,y都可”，“x可，y大于maxSPF了”，“x，y都不可”
             选择SPF最大的显然能够满足更多奶牛们的要求
              */
             if(findOne){
                 cover[maxIx]--;//用掉一瓶
                 res++;//满足一头牛
             }
         }
        System.out.println(res);
    }
}

---

2.Stall Reservations
题目链接

import java.util.Arrays;
import java.util.Comparator;
import java.util.Scanner;

public  class Main
{

    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int n;
        n=sc.nextInt();
        row x[]=new row[50000+10];
        int room[]=new int[50000+10];

        for(int i=1;i<=n;i++)
        {   x[i]=new row();
            x[i].begin=sc.nextInt();
            x[i].end=sc.nextInt();
            x[i].z=i;
        }

        Arrays.sort(x,1,n+1);
        int ans=1;

        for(int i=1;i<=n;i++)
        {  int biao=0;
           int min=999999;
            for(int j=1;j<=ans;j++)
            {
                if(room[j]<x[i].begin&&room[j]<min)
                {
                    biao=j;
                    min=room[j];
                }
            }
            if(biao==0){
                ans++;
                room[ans]=x[i].end;
                x[i].ans=ans;
            }
            else
            {
                room[biao]=x[i].end;
                x[i].ans=biao;
            }

        }

        Arrays.sort(x, 1, n + 1, new Comparator<row>() {
            @Override
            public int compare(row o1, row o2) {
                return o1.z-o2.z;
            }
        });
        System.out.println(ans);
        for(int i=1;i<=n;i++)
            System.out.println(x[i].ans);
    }



}





 class row implements Comparable<row>{
    int begin,end;
    int ans;
    int z;

    @Override
    public int compareTo(row o) {
        return begin-o.begin;
    }




}

---

3.Radar Installation
题目链接

代码:

import java.util.Arrays;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int d = sc.nextInt();
		C[] node = new C[n];
		boolean f = true;
		int x,y;
		for(int i=0;i<n;i++) {
			x = sc.nextInt();
			y = sc.nextInt();
			if(y>d) {
				f = false;
				break;
			}
			double len = Math.sqrt(d*d-y*y);
			node[i] = new C(x-len,x+len);
		}
		if(!f) {
			System.out.println(-1);
		}else {
			Arrays.sort(node);
			int ans = 0;
			double r = -1e10;
			for(int i=0;i<n;i++) {
				if(node[i].l>r+1e-6) {
					ans++;
					r = node[i].r;
				}
			}
			System.out.println(ans);
		}
	}
}	
class C implements Comparable<C>{
	double l,r;
	public C(double l,double r) {
		this.l = l;
		this.r = r;
	}
	public int compareTo(C o) {
		if(this.r>o.r)
			return 1;
		else
			return -1;
	}
}

---

4.国王的游戏
题目链接

代码:

import java.math.BigInteger;
import java.util.Arrays;
import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

// @author:jahup
public class Main {


    public static void main( String args[] ){

        Scanner sc=new Scanner(System.in);
        int n;
        final int N=10000+10;

        n=sc.nextInt();
        human all[]=new human[N];
        for(int i=1;i<=n+1;i++){
            all[i]=new human(sc.nextInt(),sc.nextInt());

        }

        Arrays.sort(all,2,n+2);

        BigInteger all_=new BigInteger("1");
        BigInteger max=new BigInteger("0");
        for(int i=1;i<=n+1;i++){
            BigInteger now_x=new BigInteger(all[i].x.toString());
            BigInteger now_y=new BigInteger(all[i].y.toString());
            max=all_.divide(now_y).compareTo(max)>0?all_.divide(now_y):max;
            all_=all_.multiply(now_x);
        }
        System.out.println(max.toString());
    }
}
class human implements Comparable<human>{
    Integer x,y;

    public human(int x, int y) {
        this.x = x;
        this.y = y;
    }

    @Override
    public int compareTo(human o) {
        return  x*y-o.x*o.y;
    }
}

---

5.Color a Tree
题目链接

代码:

import java.util.Scanner;

public class Main {
	static int n,root;
	static E[] node = new E[1005];
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		n = sc.nextInt();
		root = sc.nextInt();
		int res = 0;
		for(int i=1;i<=n;i++) {
			int a = sc.nextInt();
			node[i] = new E(i,a,1,a);
			res += a;    //每个都先是独立的点
		}
		for(int i=1;i<n;i++) {
			int a = sc.nextInt();
			int b = sc.nextInt();
			node[b].father = a;
		}
		for(int i=1;i<n;i++) {
			int p = find();   //找到均值最大的点
			int f = node[p].father; 
			res += node[p].sum*node[f].size;  //与父节点合并  添加在后面  
			node[p].avg = -1;   //与父节点已经合并  删出该点   
			for(int j=1;j<=n;j++) {   //在把该节点的子节点与新父节点连接
				if(node[j].father == p) {
					node[j].father = f;
				}
			}
			//更新父节点
			node[f].sum += node[p].sum;
			node[f].size += node[p].size;
			node[f].avg = node[f].sum*1.0/node[f].size;
		}
		System.out.println(res);
	}
	public static int find() {
		int t = 0;
		double avg = 0;
		for(int i=1;i<=n;i++) {
			if(i!=node[i].father&&avg<node[i].avg) {
				avg = node[i].avg;
				t = i;
			}
		}
		return t;
	}
}
class E{
	int father,sum,size;
	double avg;
	public E(int father,int sum,int size,double avg) {
		this.father = father;
		this.sum = sum;
		this.size = size;
		this.avg = avg;
	}
}

本文地址：https://blog.csdn.net/jahup/article/details/110236150