1. Min history
A parallel stack stores the minimum at each depth.
this.mins = []Typorithm · medium
Min Stack
min-stackstacks-queuesauxiliary-stackrunning-minconstant-time
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Full lesson · 8 learning steps Open any exercise for focused practice
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Step 1 of 8 · intro card
Learn Min Stack
Stacks & Queues
Keep a parallel stack of running minimums so getMin is O(1) at every depth.
Tracking a single min variable breaks when that min is popped off.
A parallel stack records the minimum present at each level, pushed and popped in lockstep.
The top of that min stack is the current minimum, so getMin is constant time.
01
Parallel min stack per level.
02
Push min(val, prevMin).
03
getMin reads the min stack top.
class MinStack {
constructor() {
this.stack = [];
this.mins = [];
}
push(val) {
this.stack.push(val);
const min = this.mins.length === 0
? val
: Math.min(val, this.mins[this.mins.length - 1]);
this.mins.push(min);
}
pop() {
this.stack.pop();
this.mins.pop();
}
top() {
return this.stack[this.stack.length - 1];
}
getMin() {
return this.mins[this.mins.length - 1];
}
}Read the implementation
Connect each part of the code to the concept before you type.
2. New running min
The min so far is the smaller of val and the prior min.
Math.min(val, this.mins[this.mins.length - 1])3. Pop both
Removing a value also removes its recorded min.
this.mins.pop()4. O(1) min
The top of the min stack is always the current minimum.
return this.mins[this.mins.length - 1]A complete learning loop
01
Understand
Read the concept map and follow the code breakdown.
02
Reconstruct
Type the implementation, repair mistakes and work through every recall exercise.
03
Verify
Use the final check without hints; revisit weak concepts in short practice sessions.