042.单调栈
单调栈
模板
获取每个元素左右两侧第一个大于（小于）它的元素
const int N=1e5;
int a[N];
int top,st[N],L[N],R[N];
int n;
void init(){
top=-1;
for(int r=0;r<n;++r){
while(top!=-1&&a[st[top]]<=a[r]){//第一个大于a[i]
int i=st[top--];
L[i]=top==-1?-1:st[top];
R[i]=r;
}
st[++top]=r;
}
while(top!=-1){
int i=st[top--];
L[i]=top==-1?-1:st[top];
R[i]=n;
}
//处理重复元素
for(int i=n-2;i>=0;--i){
if(R[i]!=n&&a[R[i]]==a[i]){
R[i]=R[R[i]];
}
}
}
题单
P1901
void solve(){
cin>>n;
for(int i=0;i<n;++i)cin>>a[i]>>w[i];
init();
vector<int>cnt(n);
for(int i=0;i<n;++i){
int l=L[i];
if(l!=-1)cnt[l]+=w[i];
int r=R[i];
if(r!=n)cnt[r]+=w[i];
}
int ans=-1;
for(int x:cnt)if(x>ans)ans=x;
cout<<ans;
}
P8082
void solve(){
cin>>n>>k;
string s;
cin>>s;
stack<char>st;
for(char c:s){
while(st.size()&&k&&c>st.top()){
st.pop();
k--;
}
st.push(c);
}
string ans="";
while(st.size()){
ans+=st.top();
st.pop();
}
reverse(ans.begin(),ans.end());
cout<<ans;
}
P2886
void solve(){
cin>>n;
for(int i=0;i<n;++i)cin>>a[i];
init();
long ans=0;
for(int i=0;i<n;++i){
ans+=R[i]-i-1;
}
cout<<ans;
}
P2947
void solve(){
cin>>n;
for(int i=0;i<n;++i)cin>>a[i];
init();
for(int i=0;i<n;++i){
if(R[i]==n)cout<<0<<'\n';
else cout<<R[i]+1<<'\n';
}
}
P8094
void solve(){
cin>>n;
for(int i=0;i<n;++i)cin>>a[i];
init();
ll ans=0;
for(int i=0;i<n;++i){
if(L[i]!=-1)ans+=i-L[i]+1;
if(R[i]!=n)ans+=R[i]-i+1;
}
cout<<ans;
}
P13796
typedef struct{
ll mo;//分子
ll de;//分母
}f;
ll gcd(ll a,ll b){
if(a<0)a=-a;
if(b<0)b=-b;
ll t;
while(b){
t=b;
b=a%b;
a=t;
}
return a;
}
//化简
void simp(f* x){
if(x->de<0){
x->de=-x->de;
x->mo=-x->mo;
}
ll cd=gcd(x->de,x->mo);
x->de/=cd;
x->mo/=cd;
}
void solve(){
cin>>n;
for(int i=0;i<n;++i)cin>>a[i];
init();
f ans;
ans.de=1;
ans.mo=0;
for(int i=0;i<n;++i){
int l=L[i],r=R[i];
if(l!=-1&&i-l>1){
f t;
t.mo=a[i]-a[l+1];
t.de=a[l]-a[l+1];
t.mo+=t.de*(i-l-1);
if(ans.mo*t.de<ans.de*t.mo)ans=t;
}
if(r!=n&&r-i>1){
f t;
t.mo=a[i]-a[r-1];
t.de=a[r]-a[r-1];
t.mo+=t.de*(r-i-1);
if(ans.mo*t.de<ans.de*t.mo)ans=t;
}
}
simp(&ans);
if(ans.mo==0)cout<<0;
else if(ans.de==1)cout<<ans.mo;
else cout<<ans.mo<<'/'<<ans.de;
}
P1823
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
const int N=5e5+5;
int n;
int top=-1,st[N];
struct p{
ll h;
int cnt=1;
}P[N];
void solve(){
cin>>n;
for(int i=0;i<n;++i)cin>>P[i].h;
ll ans=0;
for(int i=0;i<n;++i){
while(top!=-1&&P[st[top]].h<P[i].h){
ans+=P[st[top]].cnt;
top--;
}
if(top!=-1&&P[st[top]].h==P[i].h){
ans+=P[st[top]].cnt;
P[i].cnt+=P[st[top]].cnt;
top--;
}
if(top!=-1)ans++;
st[++top]=i;
}
cout<<ans;
}
int main(void){
cin.tie(0)->sync_with_stdio(0);
int T=1;
//cin>>T;
while(T--)solve();
}
P2422
ll pre[N]={0};
void solve(){
cin>>n;
for(int i=0;i<n;++i)cin>>a[i],pre[i+1]=pre[i]+a[i];
init();
ll ans=0;
for(int i=0;i<n;++i){
int l=L[i],r=R[i];
ll sum=pre[r]-pre[l+1];
ans=max(ans,sum*a[i]);
}
cout<<ans;
}
P3467
void solve(){
cin>>n;
int w;
for(int i=0;i<n;++i)cin>>w>>a[i];
int ans=n;
for(int i=0;i<n;++i){
while(top!=-1&&a[st[top]]>=a[i]){
if(a[st[top--]]==a[i])ans--;
}
st[++top]=i;
}
cout<<ans;
}
P2659
void solve(){
cin>>n;
for(int i=0;i<n;++i)cin>>a[i];
init();
ll ans=0;
for(int i=0;i<n;++i){
int l=L[i],r=R[i];
ans=max(ans,a[i]*(r-l-1));
}
cout<<ans;
}
P3666
void solve(){
cin>>n;
for(int i=1;i<=n;++i)cin>>a[i];
top=-1;
ll ans=0;
for(int i=1;i<=n;++i){
while(top!=-1&&a[st[top]]<=a[i]){
ans^=st[top--];
}
st[++top]=i;
ans^=i;
cout<<ans<<'\n';
}
}
42
class Solution {
public:
int trap(vector<int>& height) {
stack<int>st;
int siz=height.size();
int ans=0;
for(int r=0;r<siz;++r){
while(st.size()>1&&height[st.top()]<height[r]){
int h=st.top();
st.pop();
int w=r-st.top()-1;
ans+=w*(min(height[st.top()],height[r])-height[h]);
}
while(st.size()&&height[st.top()]<=height[r])st.pop();
st.push(r);
}
return ans;
}
};
907
const int P=1e9+7;
const int N=30005;
int L[N],R[N],st[N],top;
class Solution {
public:
int sumSubarrayMins(vector<int>& arr) {
int n=arr.size();
top=-1;
for(int r=0;r<n;++r){
while(top!=-1&&arr[st[top]]>=arr[r]){
int i=st[top--];
L[i]=top==-1?-1:st[top];
R[i]=r;
}
st[++top]=r;
}
while(top!=-1){
int i=st[top--];
L[i]=top==-1?-1:st[top];
R[i]=n;
}
long ans=0;
for(int i=0;i<n;++i){
ans=(ans+(long)(i-L[i])*(R[i]-i)%P*arr[i])%P;
}
return (int)ans;
}
};
962
class Solution {
public:
int maxWidthRamp(vector<int>& nums) {
int n=nums.size();
stack<int>st;
st.push(0);
for(int i=0;i<n-1;++i){
if(nums[i]<nums[st.top()])st.push(i);
}
int ans=0;
for(int i=n-1;i;i--){
if(st.size()&&i<st.top())break;
while(st.size()&&nums[st.top()]<=nums[i]){
ans=max(ans,i-st.top());
st.pop();
}
}
return ans;
}
};```
</details>
[leetcode 316](https://leetcode.cn/problems/remove-duplicate-letters/)
<details><summary> 316 </summary>
```cpp
class Solution {
public:
string removeDuplicateLetters(string s) {
vector<int>cnt(26),vis(26);
stack<char>st;
for(char c:s)cnt[c-'a']++;
for(char c:s){
if(vis[c-'a']){
cnt[c-'a']--;
continue;
}
while(st.size()&&st.top()>c){
if(cnt[st.top()-'a']){
vis[st.top()-'a']=0;
st.pop();
}
else{
break;
}
}
st.push(c);
cnt[c-'a']--;
vis[c-'a']=1;
}
string ans="";
while(st.size()){
ans=st.top()+ans;
st.pop();
}
return ans;
}
};
2289
class Solution {
public:
int totalSteps(vector<int>& nums) {
int n=nums.size();
stack<pair<int,int>>st;
int ans=0;
for(int i=n-1;i>=0;--i){
int cnt=0;
while(st.size()&&st.top().first<nums[i]){
cnt++;
auto [_,t]=st.top();
st.pop();
cnt=max(cnt,t);
ans=max(ans,cnt);
}
st.push({nums[i],cnt});
}
return ans;
}
};
84
class Solution {
public:
int largestRectangleArea(vector<int>& heights) {
heights.push_back(-1);
int siz=heights.size();
stack<int>st;
st.push(-1);
int ans=0;
for(int r=0;r<siz;++r){
while(st.size()>1&&heights[st.top()]>heights[r]){
int h=st.top();
st.pop();
int w=r-1-st.top();
ans=max(ans,w*heights[h]);
}
st.push(r);
}
return ans;
}
};
85
class Solution {
vector<vector<int>>H;
int get_S(int i){
int S=0;
H[i].push_back(-1);
int siz=H[i].size();
stack<int>st;
st.push(-1);
for(int r=0;r<siz;++r){
while(st.size()>1&&H[i][st.top()]>H[i][r]){
int h=st.top();
st.pop();
int w=r-1-st.top();
S=max(S,w*H[i][h]);
}
st.push(r);
}
return S;
}
public:
int maximalRectangle(vector<vector<char>>& matrix) {
int n=matrix.size(),m=matrix[0].size();
H.resize(n);
for(int i=0;i<n;++i)H[i].resize(m);
for(int i=0;i<n;++i){
for(int j=0;j<m;++j){
if(i==0)H[i][j]=matrix[i][j]-'0';
else{
if(matrix[i][j]=='0')H[i][j]=0;
else H[i][j]=H[i-1][j]+1;
}
}
}
int ans=0;
for(int i=0;i<n;++i){
ans=max(ans,get_S(i));
}
return ans;
}
};
1504
class Solution {
public:
int numSubmat(vector<vector<int>>& mat) {
int n=mat.size(),m=mat[0].size();
vector<int>st(m+1),h(m+1);
int top;
int ans=0;
for(int i=0;i<n;++i){
for(int j=0;j<m;++j){
if(mat[i][j]==0)h[j]=0;
else h[j]++;
}
top=-1;
h[m]=0;
for(int r=0;r<=m;++r){
while(top!=-1&&h[st[top]]>=h[r]){
if(h[st[top]]==h[r]){
top--;
continue;
}
int cur=st[top--];
int l=top==-1?-1:st[top];
int hl=l==-1?0:h[l];
int w=r-l-1;
int leve=h[cur]-max(hl,h[r]);
ans+=(w+1)*w/2*leve;
}
st[++top]=r;
}
}
return ans;
}
};
I am the bone of my sword
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