[Function add]

1. Add leetcode solutions.

Author: Botao Xiao

README.md

@@ -391,6 +391,10 @@
 
 [223. Rectangle Area](https://github.com/Seanforfun/Algorithm-and-Leetcode/blob/master/leetcode/223.%20Rectangle%20Area.md)
 
+[224. Basic Calculator](https://github.com/Seanforfun/Algorithm-and-Leetcode/blob/master/leetcode/224.%20Basic%20Calculator.md)
+
+[225. Implement Stack using Queues](https://github.com/Seanforfun/Algorithm-and-Leetcode/blob/master/leetcode/225.%20Implement%20Stack%20using%20Queues.md)
+
 ## Algorithm(4th_Edition)
 Reading notes of book Algorithm(4th Algorithm),ISBN: 9787115293800.
 All java realization codes are placed in different packages.

leetcode/224. Basic Calculator.md

@@ -1,21 +1,4 @@
-## 223. Rectangle Area
-
-### Question
-Find the total area covered by two rectilinear rectangles in a 2D plane.
-
-Each rectangle is defined by its bottom left corner and top right corner as shown in the figure.
-![question](https://leetcode.com/static/images/problemset/rectangle_area.png)
-```
-Example:
-
-Input: A = -3, B = 0, C = 3, D = 4, E = 0, F = -1, G = 9, H = 2
-Output: 45
-
-```
-
-### Thinking:
-* Method 1：两个长方形的面积和 - 交集的面积
-a## 224. Basic Calculator
+## 224. Basic Calculator
 
 ### Question
 Implement a basic calculator to evaluate a simple expression string.
@@ -81,16 +64,39 @@ class Solution {
     }
 }
 ```
+
+### 二刷
+1. Refer to previous answer.
 ```Java
 class Solution {
-    public int computeArea(int A, int B, int C, int D, int E, int F, int G, int H) {
-        int total  = (C - A) * (D - B) + (G - E) * (H - F);
-        if(E > C || G < A || F > D || H < B) return total;
-        else{
-            int height = Math.min(H, D) - Math.max(B, F);
-            int width = Math.min(G, C) - Math.max(A, E);
-            return total - height * width;
+    public int calculate(String s) {
+        char[] arr = s.toCharArray();
+        Stack<Integer> stack = new Stack<>();
+        int sign = 1;
+        int result = 0;
+        int len = arr.length;
+        for(int i = 0; i < arr.length; i++){
+            char c = arr[i];
+            if(Character.isDigit(c)){
+                int num = c - '0';
+                while(i + 1 < len && Character.isDigit(arr[i + 1]))
+                    num = num * 10 + (arr[++i] - '0');
+                result += num * sign;
+            }else if(c == '+'){
+                sign = 1;
+            }else if(c == '-'){
+                sign = -1;
+            }else if(c == '('){
+                stack.push(result);
+                stack.push(sign);
+                result = 0;
+                sign = 1;
+            }else if(c == ')'){
+                sign = stack.pop();
+                result = stack.pop() + sign * result;
+            }
         }
+        return result;
     }
 }
-```
+```

leetcode/225. Implement Stack using Queues.md

@@ -63,4 +63,43 @@ class MyStack {
  * int param_3 = obj.top();
  * boolean param_4 = obj.empty();
  */
-```
+```
+
+### 二刷
+1. Use LinkedList to realize stack.
+```Java
+class MyStack {
+    LinkedList<Integer> stack = null;
+    int size = 0;
+    /** Initialize your data structure here. */
+    public MyStack() {
+        stack = new LinkedList<>();
+    }
+    /** Push element x onto stack. */
+    public void push(int x) {
+        this.stack.addFirst(x);
+        this.size++;
+    }
+    /** Removes the element on top of the stack and returns that element. */
+    public int pop() {
+        this.size --;
+        return this.stack.pollFirst();
+    }
+    /** Get the top element. */
+    public int top() {
+        return this.stack.get(0);
+    }  
+    /** Returns whether the stack is empty. */
+    public boolean empty() {
+        return this.size == 0;
+    }
+}
+/**
+ * Your MyStack object will be instantiated and called as such:
+ * MyStack obj = new MyStack();
+ * obj.push(x);
+ * int param_2 = obj.pop();
+ * int param_3 = obj.top();
+ * boolean param_4 = obj.empty();
+ */
+```