zoukankan      html  css  js  c++  java
  • leetcode -- Jump Game

    Given an array of non-negative integers, you are initially positioned at the first index of the array.

    Each element in the array represents your maximum jump length at that position.

    Determine if you are able to reach the last index.

    For example:
    A = [2,3,1,1,4], return true.

    A = [3,2,1,0,4], return false.

    [解题思路]

    1.一维DP,jump[i]表示到达位置i剩余的最大步数

     1 public boolean canJump(int[] A) {
     2         // Start typing your Java solution below
     3         // DO NOT write main() function
     4         int len = A.length;
     5         //using DP
     6         int[] jump = new int[len];
     7         jump[0] = 0;
     8         
     9         for(int i = 1; i < len; i++){
    10             jump[i] = Math.max(jump[i - 1], A[i - 1]) - 1;
    11             if(jump[i] < 0){
    12                 return false;
    13             }
    14         }
    15         return true;
    16     }

     2.二维DP

    f(i)表示是否可以从position 0到达i

    f(i) = OR 'f(j) && A[j] + j >= i' j = 0,...,i - 1

    时间复杂为O(N^2), 大数据集会超时

     1 public boolean canJump(int[] A) {
     2         if(A.length == 0){
     3             return true;
     4         }
     5         int len = A.length;
     6         boolean[] f = new boolean[len];
     7         f[0] = true;
     8         for(int i = 1; i < len; i++){
     9             for(int j = 0; j < i; j++){
    10                 f[i] = f[i] || (f[j] && (A[j] + j >= i));
    11             }
    12         }
    13         return f[len - 1];
    14     }

     3.Greedy

    维护一个maxDis变量,表示当前可以到达的最大距离

    当maxDis >= len - 1表示可以到达

    每经过一点都将maxDis 与 i + A[i]进行比较,更新最大值

     1 public boolean canJump(int[] A) {
     2         if(A.length == 0){
     3             return true;
     4         }
     5         int len = A.length;
     6         int maxDis = 0;
     7         for(int i = 0; i < len; i++){
     8             
     9             if(maxDis < i){
    10                 return false;
    11             }
    12             maxDis = Math.max(maxDis, i + A[i]);
    13             if(maxDis >= len - 1){
    14                 return true;
    15             }
    16         }
    17         
    18         return false;
    19     }
  • 相关阅读:
    电话号码和手机号码正则
    IntelliJ Idea 常用快捷键
    springboot常用注解
    idea常用快捷键和插件
    百度地图API的使用方法
    js 经常用到的键盘码
    https://www.cnblogs.com/
    axios传参 后台接收为空
    面相对象之继承
    初始面向对象
  • 原文地址:https://www.cnblogs.com/feiling/p/3241934.html
Copyright © 2011-2022 走看看