Monotonic stack summary

The meaning of monotonic stack: record (element i traverses from left (right traverse) the first element k that is less than or greater than) subscript

Vernacular: (eligible) and (element k closest to element i) subscript   

The condition here means: larger than element i, or smaller than element i

The maintenance significance of the monotonic stack: ensure that the bottom f of the stack is the minimum value of the interval [0, i), and ensure that all elements of the stack are the first minimum value of [0, i), the second minimum value......

Maintained core code:

while(!p1.empty() && t[p1.top()] >= t[i])  p1.pop();

int ml[mmax];
stack<int> p1;

for(int i = 1 ; i <= n ; i ++){
        while(!p1.empty() && t[p1.top()] >= t[i])  p1.pop();
        if(p1.empty()) ml[i] = 0;
        else  ml[i] = p1.top();
        p1.push(i);
     }

Each element can only be pushed onto the stack once, and the corresponding element can only be popped once at most.

That is, the algorithm complexity: O(N)*O(1) = O(N)

for(int i = 1 ; i<= n ; i++){

O(1);

}