[LeetCode] 390. Elimination Game

flowercha

于 2016-10-23 00:53:38 发布

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分类专栏： interview preparation 文章标签： leetcode java algorithm number operation

本文链接：https://blog.youkuaiyun.com/u010500263/article/details/52896482

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本文介绍了一种解决约瑟夫环问题的算法实现，通过定义类Solution及方法lastRemaining来逐步缩小元素范围，最终返回序列中剩余的最后一个元素。算法通过调整gap值和判断剩余元素奇偶性来实现从左到右、从右到左交替删除元素的过程。

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public class Solution {
    public int lastRemaining(int n) {
        if(n < 1){
            return 0;
        }
        
        if(n==1){
            return 1;
        } 
        
        int gap = 1; // gap between 2 elements
        int res = 1;
        
        while(gap*2<=n){ // check if there is next element
            // from left to right, always delete the first element
            res += gap;
            
            // after each run through, gap *=2
            gap *= 2;
            
            // from right to left
            if(gap*2 <= n){
                // check if 1st element needs to be deleted
                if((n/gap)%2 == 1){ // only when odd numbers of elements left, we need to delete the 1st element
                    res += gap;
                }
                gap *= 2;
            }
        }
        
        return res;
    }
}