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Merge k Sorted Lists.cpp
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Merge k Sorted Lists.cpp
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/**
* 直接用最小堆或者用最小堆模拟败者树
*/
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* mergeKLists(vector<ListNode*> lists) {
// 用最小堆模拟败者树
auto f = [&](const int x, const int y)->bool{return lists[x]->val > lists[y]->val; };
priority_queue<int, vector<int>, decltype(f)> Q(f);
ListNode node(1024), *p = &node;
int k = lists.size();
// 初始化败者树
for (int i = 0; i < k; ++i) {
if (lists[i] == NULL) {
continue;
}
Q.push(i);
}
while (!Q.empty()) {
int i = Q.top();
Q.pop();
p->next = lists[i];
p = p->next;
lists[i] = lists[i]->next;
if (lists[i] != NULL) {
Q.push(i);
}
}
return node.next;
}
};
class Solution {
public:
// 败者树调整函数
void ajustLosers(int exnode[], int leaf[], int k, int i) {
int p = (i + k) >> 1;
while (p > 0) {
if (exnode[p] == -1) {
exnode[p] = i;
return;
}
if (leaf[exnode[p]] < leaf[i]) {
swap(exnode[p], i);
}
p >>= 1;
}
exnode[0] = i;
}
// 败者树建立函数
void LoserTree(int exnode[], int leaf[], int k) {
fill_n(exnode, k, -1);
for (int i = 0; i < k; ++i) {
ajustLosers(exnode, leaf, k, i);
}
}
ListNode* mergeKLists(vector<ListNode*> &lists) {
if (lists.empty()) {
return NULL;
}
ListNode node(1024), *p = &node;
int k = lists.size();
int exnode[2 * k], *leaf = exnode + k;
// 初始化败者树
for (int i = 0; i < k; ++i) {
leaf[i] = lists[i] != NULL ? lists[i]->val : INT_MAX;
}
LoserTree(exnode, leaf, k);
while (true) {
int i = exnode[0];
if (leaf[i] == INT_MAX) {
break;
}
p->next = lists[i];
p = p->next;
lists[i] = lists[i]->next;
leaf[i] = lists[i] != NULL ? lists[i]->val : INT_MAX;
ajustLosers(exnode, leaf, k, i);
}
return node.next;
}
};