[Leetcode] Frog Jump

A frog is crossing a river. The river is divided into x units and at each unit there may or may not exist a stone. The frog can jump on a stone, but it must not jump into the water.

Given a list of stones' positions (in units) in sorted ascending order, determine if the frog is able to cross the river by landing on the last stone. Initially, the frog is on the first stone and assume the first jump must be 1 unit.

If the frog's last jump was k units, then its next jump must be either k - 1, k, or k + 1 units. Note that the frog can only jump in the forward direction.

Note:

• The number of stones is ≥ 2 and is < 1,100.
• Each stone's position will be a non-negative integer < 231.
• The first stone's position is always 0.

Example 1:

[0,1,3,5,6,8,12,17]

There are a total of 8 stones.
The first stone at the 0th unit, second stone at the 1st unit,
third stone at the 3rd unit, and so on...
The last stone at the 17th unit.

Return true. The frog can jump to the last stone by jumping 
1 unit to the 2nd stone, then 2 units to the 3rd stone, then 
2 units to the 4th stone, then 3 units to the 6th stone, 
4 units to the 7th stone, and 5 units to the 8th stone.

public class Solution {
    public boolean canCross(int[] stones) {
        Set stonesSet = getSet(stones);
        Map> record = new HashMap<>();
        return canCross(0, 0, stones[stones.length - 1], stonesSet, record);
    }
    
    private Set getSet(int[] stones) {
        Set stonesSet = new HashSet<>();
        for(int stone:stones) {
            stonesSet.add(stone);
        }
        return stonesSet;
    }
    
    private boolean canCross(int preJump, int position, int target, Set stone, Map> record) {
        int his = checkRecord(preJump, position, record);
        if(his == 1){
            return true;
        }
        else if(his == -1) {
            return false;
        }
        int firstPosition = preJump + position;
        int secondPosition =  preJump + position - 1;
        int thirdPosition = preJump + position + 1;
        if(position == target) {
            saveRecord(preJump, position, record, true);
            return true;
        }
        if(firstPosition > position && stone.contains(firstPosition) && canCross(preJump, firstPosition, target, stone, record)) {
            saveRecord(preJump, position, record, true);
            return true;
        }
        if(secondPosition > position && stone.contains(secondPosition) && canCross(preJump - 1, secondPosition, target, stone, record)) {
            saveRecord(preJump, position, record, true);
            return true;
        }
        if(thirdPosition > position && stone.contains(thirdPosition) && canCross(preJump + 1, thirdPosition, target, stone, record)) {
            saveRecord(preJump, position, record, true);
            return true;
        }
        saveRecord(preJump, position, record, false);
        return false;
    }
    
    private int checkRecord(int preJump, int position, Map> record) {
        if(record.containsKey(preJump) && record.get(preJump).containsKey(position)) {
            if(record.get(preJump).get(position)) {
                return 1;
            }
            else {
                return -1;
            }
        }
        return 0;
    }
    
    private void saveRecord(int preJump, int position, Map> record, Boolean result) {
        if(record.containsKey(preJump)){
            record.get(preJump).put(position, result);
            return;
        }
        Map tmp = new HashMap<>();
        tmp.put(position, result);
        record.put(preJump, tmp);
    }
}

Kind of cleaner, but much slower:

public class Solution {
    public boolean canCross(int[] stones) {
        Map> record = new HashMap<>();
        return canCross(0, 0, stones, record);
    }
    
    private boolean canCross(int preJump, int position,int[] stone, Map> record) {
        int his = checkRecord(preJump, position, record);
        if(his == 1){
            return true;
        }
        else if(his == -1) {
            return false;
        }
        
        if(position == stone.length - 1) {
            saveRecord(preJump, position, record, true);
            return true;
        }
        for(int i = position + 1; i < stone.length; i++) {
            int dis = stone[i] - stone[position];
            if(dis == preJump || dis == preJump -1 || dis == preJump + 1) {
                if(canCross(dis, i, stone, record)){
                    return true;
                }
            }
        }
        saveRecord(preJump, position, record, false);
        return false;
    }
    
    private int checkRecord(int preJump, int position, Map> record) {
        if(record.containsKey(preJump) && record.get(preJump).containsKey(position)) {
            if(record.get(preJump).get(position)) {
                return 1;
            }
            else {
                return -1;
            }
        }
        return 0;
    }
    
    private void saveRecord(int preJump, int position, Map> record, Boolean result) {
        if(record.containsKey(preJump)){
            record.get(preJump).put(position, result);
            return;
        }
        Map tmp = new HashMap<>();
        tmp.put(position, result);
        record.put(preJump, tmp);
    }
}