zoukankan      html  css  js  c++  java
  • 403. Frog Jump

    package LeetCode_403
    
    /**
     * 403. Frog Jump
     * https://leetcode.com/problems/frog-jump/description/
     *
     * 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.
     * */
    
    class Solution {
        /*
        *                  0, 1, 3, 5, 6, 8, 12, 17
     step between two caps:  1  2  2 3(5-8) 4   5  <=we can see each step is: k, or k + 1 units
        * */
        fun canCross(stones: IntArray): Boolean {
            val size = stones.size
            for (i in size-2 downTo 0) {
                if (dfs(stones, i, stones[size-1] - stones[i])) {
                    return true
                }
            }
            return false
        }
    
        /**
         * solution:dfs, Time complexity: O(2^n), Space complexity:O(n)
         * */
        private fun dfs(stones: IntArray, index: Int, target: Int): Boolean {
            if (index == 0 && target == 1) {
                return true
            }
            for (i in index-1 downTo 0) {
                //if cap is so big, skip it and check next
                if ((stones[index] - stones[i]) > target + 1 || (stones[index] - stones[i]) < target - 1) {
                    continue
                }
                if (dfs(stones, i, stones[index] - stones[i])) {
                    return true
                }
            }
            return false
        }
    }
  • 相关阅读:
    轮叫调度(RoundRobin Scheduling)
    Python的Daemon管理器zdaemon
    How do you select a particular option in a SELECT element in jQuery? Stack Overflow
    元宵爬虫YuanXiaoSpider
    python 异步采集,网页爬虫编写 | 一步一步学python
    吉林省明日科技有限公司
    简单分析C之Curl模块同php的curl和python的pycurl模块的关系
    fputs
    v专用链接破解器 专用链接破解器
    crawler jd
  • 原文地址:https://www.cnblogs.com/johnnyzhao/p/13085105.html
Copyright © 2011-2022 走看看