Next Greater Element of a Linked List - Amazon Top Interview Questions
Problem Statement :
Given a singly linked list node, replace every node's value with the first greater node's value to its right. If a node doesn't have a next greater node, set its value to 0. Constraints n ≤ 100,000 where n is the number of nodes in node Example 1 Input node = [3, 2, 4, 5] Output [4, 4, 5, 0] Example 2 Input node = [1, 1, 1, 1] Output [0, 0, 0, 0]
Solution :
Solution in C++ :
void replace(LLNode* root, stack<int>& s) {
if (root == NULL) return;
replace(root->next, s);
while (!s.empty() and s.top() <= root->val) s.pop();
int vals = root->val;
root->val = s.empty() ? 0 : s.top();
s.push(vals);
}
LLNode* solve(LLNode* node) {
stack<int> s;
replace(node, s);
return node;
}
Solution in Python :
class Solution:
def solve(self, node):
stack = []
ans = node
while node:
while stack and node.val > stack[-1].val:
top = stack.pop()
top.val = node.val
stack.append(node)
node = node.next
for el in stack:
el.val = 0
return ans
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