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155-Min-Stack.js
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155-Min-Stack.js
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//////////////////////////////////////////////////////////////////////////////
// Two Stacks
// Time: O(1)
// Space: O(n)
// This solution uses two stacks to save the total values and the minimum
// values. Per each new value if it is less than or equal to the current
// minimum it is pushed to both stacks. We save duplicate minimum values to
// avoid the conundrum of inquiring whether the minimum value can be removed
// (i.e. when the minimum value equals the top value can it be removed or are
// there duplicate values in the main stack).
//////////////////////////////////////////////////////////////////////////////
class MinStack {
/**
* @constructor
*/
constructor() {
this.mainStack = [];
this.minStack = [];
}
/**
* @param {number} val
* @return {void}
*/
push(val) {
this.mainStack.push(val);
if (
!this.minStack.length ||
val <= this.minStack[this.minStack.length - 1]
) {
this.minStack.push(val);
}
}
/**
* @return {void}
*/
pop() {
const val = this.mainStack.pop();
if (val === this.minStack[this.minStack.length - 1]) {
this.minStack.pop();
}
}
/**
* @return {number}
*/
top() {
return this.mainStack[this.mainStack.length - 1];
}
/**
* @return {number}
*/
getMin() {
return this.minStack[this.minStack.length - 1];
}
}