*LeetCode-Candy

最新推荐文章于 2021-07-26 04:49:30 发布

原创最新推荐文章于 2021-07-26 04:49:30 发布 · 263 阅读

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本文探讨了一种名为“糖果分配”的算法问题，通过两次遍历数组的方式优化了解决方案，提高了效率。文章首先介绍了一个初步但效率较低的方法，随后提出了一种更优的解决方案，该方法仅需从前向后及从后向前各遍历一次数组即可得出结果。

一开始的思路是先把这个ratings array sort 然后从小的rating开始fix 之后fix更大的小的就不会受影响

但是排序的话就需要储存位置和rating值需要用map 废了空间还sort费时间超时了

但是也练习了一下如何sort map basing on value

public class Solution {
    public int candy(int[] ratings) {
        Map<Integer, Integer> map = new HashMap<Integer, Integer>();
        for ( int i = 0; i < ratings.length; i ++ ){
            map.put ( i, ratings[ i ] );
        }
        List<Map.Entry<Integer, Integer>> list = new LinkedList<Map.Entry<Integer, Integer>>( map.entrySet());
        Collections.sort ( list, new Comparator<Map.Entry<Integer, Integer>> (){
            public int compare ( Map.Entry<Integer, Integer> en1, Map.Entry<Integer, Integer> en2 ){
                return en1.getValue() - en2.getValue();
            }
        });
        int [ ] num = new int [ ratings.length ];
        Arrays.fill ( num, 1 );
        for ( int i = 0; i < list.size(); i ++ ){
            Map.Entry<Integer, Integer> en = list.get( i );
            int id = en.getKey();
            int left = (id - 1 >= 0 ? id - 1 : id);
            int right = (id + 1 < ratings.length ? id + 1  : id);
            if ( ratings [ left ] < ratings [ id ] && ratings [ right ] < ratings [ id ] ){
                num [ id ] = Math.max ( num [left], num [right] ) + 1;
            }
            else if ( ratings [ left ] < ratings [ id ] )
                num [ id ] = num [ left ] + 1;
            else if ( ratings[ right ] < ratings [ id ] )
                num [ id ] = num [ right ] + 1;
        }
        int res = 0;
        for ( int i : num )
            res += i;
        return res;
    }
}

后来发现正着扫一遍再反着扫一遍就可以了每次只看前一个数字

public class Solution {
    public int candy(int[] ratings) {
        if ( ratings == null || ratings.length == 0 )
            return 0;
        int [] num = new int [ ratings.length ];
        Arrays.fill ( num, 1 );
        for ( int i = 1; i < ratings.length; i ++ ){
            if ( ratings [ i ] > ratings [ i - 1 ] )
                num [ i ] = num [ i - 1 ] + 1;
        }
        for ( int i = ratings.length - 2; i >= 0; i -- ){
            if ( ratings [ i ] > ratings [ i + 1 ] && num [ i ] <= num [ i + 1 ] )
                num [ i ] = num [ i + 1 ] + 1;
        }
        int res = 0;
        for ( int n : num )
            res += n;
        return res;
    }
}