usaco 4.3.1 Buy Low, Buy Lower

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/*ID: daniel.20LANG: JAVATASK: buylow*/ import java.util.*;import java.io.*;import java.math.BigInteger; class problem2{    StringBuilder sb = new StringBuilder();    int n;    int stocks[];    int dp[];    BigInteger arr[];    long start = System.currentTimeMillis();      int max = 1; BigInteger result=BigInteger.ZERO;    void solver() throws IOException{               BufferedReader reader = new BufferedReader(new FileReader("buylow.in"));        StringTokenizer st = new StringTokenizer(reader.readLine());        n = Integer.valueOf(st.nextToken());        stocks = new int[n];        dp = new int[n];        arr = new BigInteger[n];        Arrays.fill(dp, 1);        Arrays.fill(arr, BigInteger.ZERO);        arr[0] = BigInteger.ONE;        String tmp; int len=0;        while((tmp=reader.readLine())!=null){            st = new StringTokenizer(tmp);            while(st.hasMoreTokens()){                stocks[len++]=Integer.valueOf(st.nextToken());            }        }        for(int i=1;i<n;i++){            for(int j=0;j<i;j++){                if(stocks[j]>stocks[i]){                    if(dp[i]<dp[j]+1){                        dp[i]=dp[j]+1;                    }                }            }            HashMap<Integer,BigInteger> map = new HashMap<Integer,BigInteger>();            for(int j=0;j<i;j++){                if(stocks[j]>stocks[i]){                    if(dp[i]==dp[j]+1){                        int item = stocks[j];                        if(!map.containsKey(item)){                            arr[i]=arr[i].add(arr[j]);                            map.put(item, arr[j]);                        }else if(arr[j].compareTo(map.get(item))>0){                            arr[i]=arr[i].subtract(map.get(item));                            arr[i]=arr[i].add(arr[j]);                            map.put(item, arr[j]);                        }                                                }                }            }            if(arr[i].compareTo(BigInteger.ZERO)==0) arr[i]=BigInteger.ONE;            if(dp[i]>max){                max = dp[i];            }        }          HashMap<Integer,BigInteger> map1 = new HashMap<Integer,BigInteger>();        for(int i=0;i<n;i++){            if(dp[i]==max){                int temp = stocks[i];                if(!map1.containsKey(temp)){                    result=result.add(arr[i]);                    map1.put(temp, arr[i]);                }else if(arr[i].compareTo(map1.get(temp))>0){                    result=result.subtract(map1.get(temp));                    result=result.add(arr[i]);                    map1.put(temp, arr[i]);                }            }        }        sb.append(max).append(" ").append(result);        PrintWriter pw = new PrintWriter(new BufferedWriter(new FileWriter("buylow.out")));        System.out.println(sb.toString());        pw.println(sb.toString());         pw.close();         System.out.println("$:"+(System.currentTimeMillis()-start));        System.exit(0);             }}public class buylow {    public static void main(String[] args) throws Exception {        problem2 p = new problem2();        p.solver();    }}

终于有会做的题了。。。

练了这么多DP，这种最基础的就是送了

比较讨厌的是要计算所有唯一的路径，就是在算总数的过程中，相同终点，并且相同长度的保留最长的

其实长的一定覆盖了短的。用了个吊hashmap强行写的

然后数据太大，必须要用BigInteger，这就是java的好处了，估计C++的longlong过不去吧

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