2D版frog jump，規(guī)定跳躍方向是右或下方。
基本的思路就是依次動(dòng)態(tài)規(guī)劃，沒(méi)有什么不同。只是需要兩個(gè)map來(lái)對(duì)每個(gè)石頭進(jìn)行行和列的索引。
下面的代碼我也沒(méi)有檢查，嗯。
package snapchat;
import java.util.*;
public class FrogJump2D {
class Point{
int x;
int y;
Point(int x, int y){
this.x = x;
this.y = y;
}
}
public boolean canCross(List<int[]> stones){
Map<Integer,Map<Integer,Point>> rowsDic = new TreeMap<>();
Map<Integer,Map<Integer,Point>> colsDic = new TreeMap<>();
Map<Point,Set<Integer>> mp = new HashMap<>();
for(int[] stone : stones){
int x = stone[0];
int y = stone[1];
Point p = new Point(x,y);
if(!rowsDic.containsKey(x))rowsDic.put(x,new TreeMap<Integer, Point>());
if(!colsDic.containsKey(y))colsDic.put(y,new TreeMap<Integer, Point>());
rowsDic.get(x).put(y,p);
colsDic.get(y).put(x,p);
mp.put(p,new HashSet<Integer>());
}
if(stones.size() <= 1)return true;
Point start = rowsDic.get(0).get(0);
mp.get(start).add(0);
int[] last = stones.get(stones.size() - 1);
Point end = rowsDic.get(last[0]).get(last[1]);
for(int row : rowsDic.keySet()){
for(int col : rowsDic.get(row).keySet()){
Point p = rowsDic.get(row).get(col);
for(int step : mp.get(p)){
int[] d = new int[]{-1,0,1};
for(int i = 0; i < 3; i++){
int hor = step + col + d[i];
int ver = step + row - 1;
if(hor > col && rowsDic.get(row).containsKey(hor)){
Point hp = rowsDic.get(row).get(hor);
mp.get(hp).add(step + d[i]);
}
if(ver > row && colsDic.get(col).containsKey(ver)){
Point vp = colsDic.get(col).get(ver);
mp.get(vp).add(step + d[i]);
}
}
}
}
}
return mp.get(end).size() != 0;
}
}
