Implementation and optimization of the minimum stack

Https://mp.weixin.qq.com/s/q5wtEXg_tC-wlyK1uMlJJA Minimum Stack

Implement a minimal stack, step by step optimization, Space O (N) time O (1).

import Java.util.arraylist;import java.util.List;/** * @author Xiaoshi on 2018/9/1.*/ Public classMinstack {Privatelist<integer> data =NewArraylist<integer>(); Privatelist<integer> mins =NewArraylist<integer>();  Public voidPushintnum)        {data.add (num); if(mins.size () = =0) {            //Initialize minsmins.add (num); } Else {            //secondary stack mins The minimum value per push            intMin =getmin (); if(Num >=min)            {mins.add (min); } Else{mins.add (num); }        }    }     Public intpop () {//stack null, exception, return-1        if(data.size () = =0) {            return-1; }        //pop when two stacks sync popsMins.remove (Mins.size ()-1); returnData.remove (Data.size ()-1); }     Public intgetmin () {//stack null, exception, return-1        if(mins.size () = =0) {            return-1; }        //returns the top element of the mins stack        returnmins.Get(Mins.size ()-1); }}

[Algorithm optimization]

Time complexity O (1) space complexity is less than the preceding section of code. ,,, push pop top getMin are all O (1) time.

import Java.util.arraylist;import java.util.List;/** * @author Xiaoshi on 2018/9/1.*/ Public classMinstack {Privatelist<integer> data =NewArraylist<integer>(); Privatelist<integer> mins =NewArraylist<integer>();  Public voidPushintnum) throws Exception {data.add (num); if(mins.size () = =0) {            //Initialize minsMins.add (0); } Else {            //index of the secondary stack mins push minimum value            intMin =getmin (); if(Num <min) {Mins.add (data.size ()-1); }        }    }     Public intpop () throws Exception {//stack empty, throw exception        if(data.size () = =0) {            Throw NewException ("stack is empty"); }        //Get index first when pop        intPopindex = Data.size ()-1; //gets the top element of the mins stack, which is the minimum value index        intMinindex = mins.Get(Mins.size ()-1); //if the index of the pop goes out is the minimum index, mins only out of the stack        if(Popindex = =Minindex) {Mins.remove (mins.size ()-1); }        returnData.remove (Data.size ()-1); }     Public intGetmin () throws Exception {//stack empty, throw exception        if(data.size () = =0) {            Throw NewException ("stack is empty"); }        //gets the top element of the mins stack, which is the minimum value index        intMinindex = mins.Get(Mins.size ()-1); returnData.Get(Minindex); }}

Implementation and optimization of the minimum stack