Min Stack
Min Stack
Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.
- push(x) -- Push element x onto stack.
- pop() -- Removes the element on top of the stack.
- top() -- Get the top element.
- getMin() -- Retrieve the minimum element in the stack.
1 class MinStack { 2 List<Integer> stack = new ArrayList<Integer>(); 3 int top = -1; 4 int min = Integer.MAX_VALUE; 5 6 public void push(int x) { 7 top++; 8 stack.add(x); 9 if(min > x){ 10 min = x; 11 12 } 13 14 } 15 16 public void pop() { 17 18 int element = stack.remove(top--); 19 if(element == min) 20 { 21 updateMin(); 22 23 } 24 } 25 26 public int top() { 27 int result = stack.get(top); 28 29 return result; 30 } 31 32 public int getMin() { 33 34 return this.min; 35 } 36 public void updateMin(){ 37 if(top == -1) 38 { 39 min = Integer.MAX_VALUE; 40 return; 41 } 42 min = stack.get(0); 43 for(int i = 1; i <= top; i++){ 44 if(min > stack.get(i)) 45 min = stack.get(i); 46 } 47 } 48 }
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