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  • LeetCode 294. Flip Game II

    原题链接在这里:https://leetcode.com/problems/flip-game-ii/

    题目:

    You are playing the following Flip Game with your friend: Given a string that contains only these two characters: + and -, you and your friend take turns to flip two consecutive "++" into "--". The game ends when a person can no longer make a move and therefore the other person will be the winner.

    Write a function to determine if the starting player can guarantee a win.

    For example, given s = "++++", return true. The starting player can guarantee a win by flipping the middle "++" to become "+--+".

    Follow up:
    Derive your algorithm's runtime complexity.

    题解:

    若是有一段"++", 剩下的段和"--"组合 can not win, 那么返回true.

    从头到尾试遍了没找到这么一段"++", 返回false.

    Time Complexity: exponential.

    T(n) = (n-2) * T(n-2) = (n-2) * (n-4) * T(n-4) = O(n!!)

    AC Java:

     1 public class Solution {
     2     public boolean canWin(String s) {
     3         for(int i = 1; i<s.length(); i++){
     4             if(s.charAt(i) == '+' && s.charAt(i-1) == '+' && !canWin(s.substring(0, i-1) + "--" + s.substring(i+1))){
     5                 return true;
     6             }
     7         }
     8         return false;
     9     }
    10 }

    类似Flip Game.

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  • 原文地址:https://www.cnblogs.com/Dylan-Java-NYC/p/5186280.html
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