算法分析

初始化：f[0][2] = f[0][1] = 0，f[0][0] = -INF， 因为在第0个股票一定是无货的，必定从这个位置开始转移才有效

时间复杂度 $O(n)$

参考文献

算法提高课

Java 代码

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {
    static int N = 100010, INF = 0x3f3f3f3f;
    static int n;
    static int[] w = new int[N];
    static int[][] f = new int[N][3];
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        n = Integer.parseInt(br.readLine());

        String[] s1 = br.readLine().split(" ");
        for(int i = 1;i <= n;i ++) w[i] = Integer.parseInt(s1[i - 1]);

        f[0][2] = f[0][1] = 0; f[0][0] = -INF;
        for(int i = 1;i <= n;i ++)
        {
            f[i][0] = Math.max(f[i - 1][0], f[i - 1][2] - w[i]);
            f[i][1] = f[i - 1][0] + w[i];
            f[i][2] = Math.max(f[i - 1][1], f[i - 1][2]);
        }
        System.out.println(Math.max(f[n][1], f[n][2]));
    }
}