Nested List Weight Sum II

最新推荐文章于 2023-02-04 19:33:22 发布

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本文介绍了一种针对嵌套整数列表求和的算法，该算法首先计算列表的最大深度，然后根据深度对列表中的每个元素进行加权求和。通过递归方式处理嵌套结构，实现了逆序加权求和的功能。

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学习了一种，先算最大的深度，再计算的思路。

/**
 * // This is the interface that allows for creating nested lists.
 * // You should not implement it, or speculate about its implementation
 * public interface NestedInteger {
 *
 *     // @return true if this NestedInteger holds a single integer, rather than a nested list.
 *     public boolean isInteger();
 *
 *     // @return the single integer that this NestedInteger holds, if it holds a single integer
 *     // Return null if this NestedInteger holds a nested list
 *     public Integer getInteger();
 *
 *     // @return the nested list that this NestedInteger holds, if it holds a nested list
 *     // Return null if this NestedInteger holds a single integer
 *     public List<NestedInteger> getList();
 * }
 */
public class Solution {
    public int depthSumInverse(List<NestedInteger> nestedList) {
        int maxDepth = 1;
        if (nestedList == null || nestedList.size() == 0) {
            return 0;
        }
        maxDepth = maxDepth(nestedList, maxDepth);
        int res = sum(nestedList, maxDepth);
        return res;
    }
    
    private int sum(List<NestedInteger> nestedList, int depth) {
        int sum = 0;
        for (NestedInteger nestedInteger: nestedList) {
            if (nestedInteger.isInteger()) {
                sum = sum + nestedInteger.getInteger() * depth;
            } else {
                sum = sum + sum(nestedInteger.getList(), depth - 1);
            }
        }
        return sum;
    }
    
    private int maxDepth(List<NestedInteger> nestedList, int depth) {
        int max = depth;
        for (NestedInteger nestedInteger: nestedList) {
            if (!nestedInteger.isInteger()) {
                max = Math.max(max, maxDepth(nestedInteger.getList(), depth + 1));
            }
        }
        return max;
    }
}