⭐️个人主页：@小羊 ⭐️所属专栏：LeetCode 热题 100 很荣幸您能阅读我的文章，诚请评论指点，欢迎欢迎 ~
目录
栈
有效的括号
cpp
class Solution {
public:
bool isValid(string s) {
stack<char> st;
for (char e : s)
{
if (st.empty()) st.push(e);
else if (st.top() == '(' && e == ')' || st.top() == '{' && e == '}'
|| st.top() == '[' && e == ']') st.pop();
else st.push(e);
}
return st.empty();
}
};最小栈
cpp
class MinStack {
stack<int> st;
stack<int> minst;
public:
MinStack() {
}
void push(int val) {
st.push(val);
if (minst.empty() || val <= minst.top())
{
minst.push(val);
}
}
void pop() {
if (st.top() == minst.top())
{
minst.pop();
}
st.pop();
}
int top() {
return st.top();
}
int getMin() {
return minst.top();
}
};字符串解码
cpp
class Solution {
public:
string decodeString(string s) {
int i = 0;
return dfs(s, i);
}
string dfs(const string& s, int& i)
{
string str;
while (i < s.size() && s[i] != ']')
{
if (isdigit(s[i]))
{
int num = 0;
while (i < s.size() && s[i] != '[')
{
num = num * 10 + s[i++] - '0';
}
i++; // 跳过'['
string tmp = dfs(s, i);
i++; // 跳过']'
while (num--) str += tmp;
}
else str += s[i++];
}
return str;
}
};每日温度
cpp
class Solution {
public:
vector<int> dailyTemperatures(vector<int>& temperatures) {
int n = temperatures.size();
stack<int> st;
vector<int> res(n);
for (int i = 0; i < n; i++)
{
while (st.size() && temperatures[st.top()] < temperatures[i])
{
int t = st.top();
st.pop();
res[t] = i - t;
}
st.push(i);
}
return res;
}
};柱状图中最大的矩形
- 单调递增栈：分别从左向右和从右向左遍历，找到每个柱子左边和右边第一个比它矮的柱子位置。
- 计算宽度：对于每个柱子，其左右边界之间的距离即为矩形的宽度，高度为当前柱子的高度。
- 求最大值：遍历所有可能的矩形，找出面积最大的一个。
单调栈。
cpp
class Solution {
public:
int largestRectangleArea(vector<int>& heights) {
int n = heights.size();
vector<int> left(n), right(n);
stack<int> st;
for (int i = 0; i < n; i++)
{
while (st.size() && heights[st.top()] >= heights[i])
{
st.pop();
}
left[i] = st.empty() ? -1 : st.top();
st.push(i);
}
st = stack<int>();
for (int i = n - 1; i >= 0; i--)
{
while (st.size() && heights[st.top()] >= heights[i])
{
st.pop();
}
right[i] = st.empty() ? n : st.top();
st.push(i);
}
int res = 0;
for (int i = 0; i < n; i++)
{
res = max(res, (right[i] - left[i] - 1) * heights[i]);
}
return res;
}
};优化。
cpp
class Solution {
public:
int largestRectangleArea(vector<int>& heights) {
int n = heights.size();
vector<int> left(n, -1), right(n, n);
stack<int> st;
for (int i = 0; i < n; i++)
{
while (st.size() && heights[st.top()] > heights[i])
{
right[st.top()] = i;
st.pop();
}
if (st.size()) left[i] = st.top();
st.push(i);
}
int res = 0;
for (int i = 0; i < n; i++)
{
res = max(res, (right[i] - left[i] - 1) * heights[i]);
}
return res;
}
};堆
数组中的第K个最大元素
建堆。
cpp
class Solution {
public:
int findKthLargest(vector<int>& nums, int k) {
int n = nums.size();
for (int i = n - 2 / 2; i >= 0; i--)
{
adjust_down(nums, i, n);
}
while (--k)
{
swap(nums[0], nums[--n]);
adjust_down(nums, 0, n);
}
return nums[0];
}
void adjust_down(vector<int>& nums, int parent, int n)
{
int child = 2 * parent + 1;
while (child < n)
{
if (child + 1 < n && nums[child + 1] > nums[child]) child++;
if (nums[child] > nums[parent])
{
swap(nums[child], nums[parent]);
parent = child;
child = 2 * parent + 1;
}
else break;
}
}
};快速选择。
cpp
class Solution {
public:
int findKthLargest(vector<int>& nums, int k) {
srand(time(nullptr));
return qsort(nums, 0, nums.size() - 1, k);
}
int qsort(vector<int>& nums, int l, int r, int k)
{
if (l >= r) return nums[l];
int key = nums[rand() % (r - l + 1) + l];
int i = l, left = l - 1, right = r + 1;
while (i < right)
{
if (nums[i] < key) swap(nums[++left], nums[i++]);
else if (nums[i] == key) i++;
else swap(nums[--right], nums[i]);
}
int x = r - right + 1, y = right - left - 1;
if (x >= k) return qsort(nums, right, r, k);
else if (x + y >= k) return key;
else return qsort(nums, l, left, k - x - y);
}
};前 K 个高频元素
建小堆，找出前K的最大的。
cpp
class Solution {
using pii = pair<int, int>;
struct cmp{
bool operator()(const pii& p1, const pii& p2)
{
return p1.second > p2.second;
}
};
public:
vector<int> topKFrequent(vector<int>& nums, int k) {
unordered_map<int, int> hashmap;
for (auto e : nums) hashmap[e]++;
priority_queue<pii, vector<pii>, cmp> pq;
for (auto& [a, b] : hashmap)
{
if (pq.size() == k)
{
if (b > pq.top().second)
{
pq.pop();
pq.emplace(a, b);
}
}
else pq.emplace(a, b);
}
vector<int> res;
while (pq.size())
{
res.push_back(pq.top().first);
pq.pop();
}
return res;
}
};数据流的中位数
cpp
class MedianFinder {
priority_queue<int> left;
priority_queue<int, vector<int>, greater<int>> right;
public:
MedianFinder() {
}
void addNum(int num) {
if (left.size() == right.size())
{
if (left.size() && num <= left.top()) left.push(num);
else
{
right.push(num);
left.push(right.top());
right.pop();
}
}
else{
if (num >= left.top()) right.push(num);
else{
left.push(num);
right.push(left.top());
left.pop();
}
}
}
double findMedian() {
if (left.size() == right.size()) return (left.top() + right.top()) / 2.0;
else return left.top();
}
};本篇文章的分享就到这里了，如果您觉得在本文有所收获，还请留下您的三连支持哦~
