stack applications and increased sequence

Author: zhongn2

Largest Rectangle in Histogram.java

@@ -0,0 +1,19 @@
+public class Solution {
+    public int largestRectangleArea(int[] height) {
+        if(height.length == 0){
+            return 0;
+        }
+        Stack<Integer> stack = new Stack<Integer>();//record the index of block
+        int max = 0;
+        for(int i = 0; i <= height.length; i++){
+            int curr = (i == height.length) ? -1 : height[i];
+            while(!stack.isEmpty() && curr <= height[stack.peek()]){
+                int h = height[stack.pop()];
+                int w = stack.isEmpty()? i : i - stack.peek() - 1;
+                max = Math.max(max, h * w);
+            }
+            stack.push(i);
+        }
+        return max;
+    }
+}

Min_stack.java

@@ -0,0 +1,45 @@
+import java.util.Stack;
+
+//Min_stack
+// using two stacks to implement a minstack
+// the first stack is to store numbers, the other one is to store the min number from 1st stack
+
+public class minstack{
+	private Stack<Integer> stack1; 
+	private Stack<Integer> min_stack; 
+	// copy constructor
+	public minstack(){
+		stack1 = new Stack<Integer>();
+		min_stack = new Stack<Integer>();
+	}
+	
+	public void push(int number){
+		stack1.push(number);
+		if(min_stack.empty()){
+			min_stack.push(number);
+		}else{
+			if(min_stack.peek() >= number){
+				min_stack.push(number);
+			}
+		}
+	}
+	public int pop(){
+		if(stack1.peek() == min_stack.peek()){
+			min_stack.pop();
+		}
+		return stack1.pop();
+	}
+	public int min(){
+		return min_stack.peek();
+	}
+	public static void main(String[] args){
+		minstack minstack = new minstack();
+		minstack.push(2);
+		minstack.push(4);
+		minstack.push(10);
+		minstack.push(3);
+		minstack.pop();
+		System.out.println(minstack.min());
+	}
+}
+