招行题解

import java.util.Arrays; import java.util.Scanner; public class wain { public static void main(String args[]){
        Scanner in =new Scanner(System.in); while (in.hasNext()) { int n = in.nextInt(); int arr[]=new int[n]; for (int i=0;i<n;i++){
                arr[i]=in.nextInt();
            }
            Arrays.sort(arr); for (int i=0;i<n;i++){ if(arr[i]!=i){
                    System.out.println(i); break;
                }
            }
        }
    }
}
p2:BFS+记录hashset：
import java.util.*; import java.util.Arrays; public class xain { public static void main(String args[]){
        Scanner in =new Scanner(System.in); while (in.hasNext()) { int x = in.nextInt();
            System.out.println(find(x));
        }
    } public static int find(int x){
        Queue<Integer> queue =new LinkedList<>();
        HashSet<Integer> set=new HashSet<>();
        set.add(0);
        queue.offer(0); int step=0; while (!queue.isEmpty()){ int size=queue.size(); for (int i=0;i<size;i++){ int now=queue.poll(); if(now==x){ return step;
                } if(!set.contains(now-1)) {
                    queue.offer(now-1);
                    set.add(now-1);
                } if(!set.contains(now+1)) {
                    queue.offer(now + 1);
                    set.add(now+1);
                } if(!set.contains(now*2)) {
                    queue.offer(2 * now);
                    set.add(now*2);
                }
            }
            step++;
        } return 0;
    }
}
p3:丑数动态规划
import java.util.*; public class Main { public static void main(String args[]){
        Scanner in =new Scanner(System.in); while (in.hasNext()) { int n = in.nextInt();
           System.out.println(find(n));
            }
    } public static int find(int x){ int [] zhiyinshu= new int[3]; int [] dp=new int[x];
        dp[0]=1; int a=2,b=3,c=5; for (int i=1;i<x;i++){ int min=Math.min(a,Math.min(b,c));
            dp[i]=min; if(a==min){
                a=2*dp[++zhiyinshu[0]];
            } if(b==min){
                b=3*dp[++zhiyinshu[1]];
            } if(c==min){
                c=5*dp[++zhiyinshu[2]];
            }
        } return dp[x-1];
    }
    }