Cola Machine, Java

Cola Machine

//'main' method must be in a class 'Rextester'.
//Compiler version 1.8.0_111

import java.util.*;
import java.lang.*;

class Rextester {  
    public static void main(String args[]) {
        List<Interval> buttons = Arrays.asList(
            new Interval(100, 120),
            new Interval(200, 240),
            new Interval(400, 410)
        );
        Solution sol = new Solution();
        System.out.println(sol.colaMachine(buttons, new Interval(200, 360)));
    }
}

class Solution {
    List<Interval> buttons;
    Interval target;
    public boolean colaMachine(List<Interval> buttons, Interval target) {
        this.buttons = buttons;
        this.target = target;
        for (int i = 0; i < buttons.size(); i++) {
            // make sure you have to prcess some button
            // so target start from zero won't be classified as true
            if (DFS(i, buttons.get(i).start, buttons.get(i).end)) return true;
        }
        return false;
    }

private boolean DFS(int fromIndex, int start, int end) {
        System.out.format("%d, %d, %d\n", fromIndex, start, end);
        if (start >= target.start && end <= target.end) return true;
        if (fromIndex == buttons.size()) return false;
        if (end - start <= target.end - target.start && end <= target.end) {
            if (DFS(fromIndex + 1, start, end)) return true;
            start += buttons.get(fromIndex).start;
            end += buttons.get(fromIndex).end;
            if (DFS(fromIndex, start, end)) return true;
        }
        return false;
    }
}

class Interval {
    int start, end;
    public Interval (int s, int e) {
        start = s;
        end = e;
    }
}


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