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RobotWalkProblem.java
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131 lines (81 loc) · 2.16 KB
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public class RobotWalkProblem{
public static int robotWalk1(int N,int start,int end,int rest){
return process1(N,start,end,rest);
}
public static int process1(int N,int cur,int end,int rest){
if(rest ==0){
return cur == end ? 1 : 0;
}
else if(cur == 0){
return process1(N,1,end,rest-1);
}else
if(cur == N){
return process1(N,N-1,end,rest-1);
}else{
return process1(N,cur-1,end,rest-1)+process1(N,cur+1,end,rest-1);
}
}
public static int robotWalk2(int N,int start,int end,int rest){
int[][] dp=new int[N+1][rest+1];
for (int i=0;i<=N ;i++ ) {
for (int j=0; j<=rest; j++) {
dp[i][j]=-1;
}
}
return process2(N,start,end,rest,dp);
}
public static int process2(int N,int cur,int end,int rest,int[][] dp){
if(dp[cur][rest]!=-1){
return dp[cur][rest];
}
int ans=0;
if(rest ==0){
ans= cur == end ? 1 : 0;
}
else if(cur == 0){
ans= process2(N,1,end,rest-1,dp);
}else
if(cur == N){
ans= process2(N,N-1,end,rest-1,dp);
}else{
ans= process2(N,cur-1,end,rest-1,dp)+process2(N,cur+1,end,rest-1,dp);
}
dp[cur][rest]=ans;
return ans;
}
public static int robotWalk3(int N,int start,int end,int step){
int[][] dp=new int[N+1][step+1];
//这里初始化的是第一列
//则说明：
//在后面的双重循环中，都是按照列的顺序，从左往右初始化
for (int cur=0;cur<=N ;cur++ ) {
dp[cur][0]= cur==end?1:0;
}
//按照列的顺序，从左往右初始化，第0列已经初始化
//从第1列出发，将0-N行的第一列初始化，以此类推
for (int rest=1; rest<=step;rest++) {
for (int cur=0;cur<=N ;cur++ ) {
int ans=0;
if(cur == 0){
ans= dp[1][rest-1];
}else
if(cur == N){
ans= dp[N-1][rest-1];
}else{
ans= dp[cur-1][rest-1]+dp[cur+1][rest-1];
}
dp[cur][rest]=ans;
}
}
return dp[start][step];
}
public static void main(String[] args){
int N=4;
int start=2;
int end=4;
int rest=8;
System.out.println("count = "+robotWalk1(N,start,end,rest));
System.out.println("count = "+robotWalk2(N,start,end,rest));
System.out.println("count = "+robotWalk3(N,start,end,rest));
}
}