05 August 2008
Given a nested list of integers, return the sum of all integers in the list weighted by their depth.
Each element is either an integer, or a list – whose elements may also be integers or other lists.
Example 1:
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Input: [[1,1],2,[1,1]]
Output: 10 Explanation: Four 1's at depth 2, one 2 at depth 1.
Example 2:
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Input: [1,[4,[6]]] Output: 27
Explanation: One 1 at depth 1, one 4 at depth 2, and one 6 at depth 3; 1 + 42 + 63 = 27.
看到嵌套，会想到用递归或者Stack或者Queue，这道题就是题目给的API需要读一下，面试中可能需要自己设计和封装这些API。
递归DFS
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/**
* // This is the interface that allows for creating nested lists.
* // You should not implement it, or speculate about its implementation
* public interface NestedInteger {
* // Constructor initializes an empty nested list.
* public NestedInteger();
*
* // Constructor initializes a single integer.
* public NestedInteger(int value);
*
* // @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();
*
* // Set this NestedInteger to hold a single integer.
* public void setInteger(int value);
*
* // Set this NestedInteger to hold a nested list and adds a nested integer to it.
* public void add(NestedInteger ni);
*
* // @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();
* }
*/
class Solution {
int result;
public int depthSum(List<NestedInteger> nestedList) {
result = 0;
dfs(nestedList, 1);
return result;
}
private void dfs(List<NestedInteger> nestedList, int depth) {
for (NestedInteger ni : nestedList) {
if (ni.isInteger()) {
result += ni.getInteger() * depth;
} else {
dfs(ni.getList(), depth + 1);
}
}
}
}
Queue BFS
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class Solution {
public int depthSum(List<NestedInteger> nestedList) {
if(nestedList == null || nestedList.size() == 0) {
return 0;
}
Queue<NestedInteger> q = new LinkedList<>();
for(NestedInteger element : nestedList) {
q.offer(element);
}
int depth = 0, sum = 0;
// 标准BFS遍历
while(!q.isEmpty()) {
depth++;
int size = q.size();
for(int i = 0; i < size; i++) {
NestedInteger cur = q.poll();
if(cur.isInteger()) {
sum += depth * cur.getInteger();
}else {
List<NestedInteger> tmp = cur.getList();
for(NestedInteger element : tmp) {
q.offer(element);
}
}
}
}
return sum;
}
}