add 155

Author: shishishu

README.md

@@ -14,4 +14,5 @@ Date | Question | Python| Java | Tag | Difficulty | Remark
 20191027|[509. Fibonacci Number](https://leetcode.com/problems/fibonacci-number/)|[509p](https://github.com/shishishu/leetcode-python-java/blob/master/ipynb_files/509_Fibonacci_Number.ipynb)|[509j](https://github.com/shishishu/leetcode-python-java/blob/master/java_codes/509/Solution.java)|DP|Easy
 20191110|[3. Longest Substring Without Repeating Characters](https://leetcode.com/problems/longest-substring-without-repeating-characters/)|[003p](https://github.com/shishishu/leetcode-python-java/blob/master/ipynb_files/003_Longest_Substring_Without_Repeating_Characters.ipynb)|[003j](https://github.com/shishishu/leetcode-python-java/blob/master/java_codes/003/Solution.java)|String|Medium
 20191117|[206. Reverse Linked List](https://leetcode.com/problems/reverse-linked-list/)|[206p](https://github.com/shishishu/leetcode-python-java/blob/master/ipynb_files/206_Reverse_Linked_List.ipynb)|[206j](https://github.com/shishishu/leetcode-python-java/blob/master/java_codes/206/Solution.java)|List|Easy
-20191117|[147. Insertion Sort List](https://leetcode.com/problems/insertion-sort-list/)|[147p](https://github.com/shishishu/leetcode-python-java/blob/master/ipynb_files/147_Insertion_Sort_List.ipynb)|[147j](https://github.com/shishishu/leetcode-python-java/blob/master/java_codes/147/Solution.java)|Sort|Medium
+20191117|[147. Insertion Sort List](https://leetcode.com/problems/insertion-sort-list/)|[147p](https://github.com/shishishu/leetcode-python-java/blob/master/ipynb_files/147_Insertion_Sort_List.ipynb)|[147j](https://github.com/shishishu/leetcode-python-java/blob/master/java_codes/147/Solution.java)|Sort|Medium
+20191124|[155. Min Stack](https://leetcode.com/problems/min-stack/)|[155p](https://github.com/shishishu/leetcode-python-java/blob/master/ipynb_files/155_Min_Stack.ipynb)|[155j](https://github.com/shishishu/leetcode-python-java/blob/master/java_codes/155/Solution.java)|Stack|Easy

images/155_Q.PNG

@@ -0,0 +1,44 @@
+import java.util.Stack;
+
+class MinStack {
+
+    int min;
+    Stack<Integer> stack;
+
+    /** initialize your data structure here. */
+    public MinStack() {
+        min = Integer.MAX_VALUE;
+        stack = new Stack<Integer>();
+    }
+
+    public void push(int x) {
+        if (x <= min){
+            stack.push(min);
+            min = x;
+        }
+        stack.push(x);
+    }
+
+    public void pop() {
+        if (stack.pop() == min){
+             min = stack.pop();
+        }
+    }
+
+    public int top() {
+        return stack.peek();
+    }
+
+    public int getMin() {
+        return min;
+    }
+}
+
+/**
+ * Your MinStack object will be instantiated and called as such:
+ * MinStack obj = new MinStack();
+ * obj.push(x);
+ * obj.pop();
+ * int param_3 = obj.top();
+ * int param_4 = obj.getMin();
+ */

images/155_S1.PNG

@@ -15,6 +15,7 @@
       <sourceFolder url="file://$MODULE_DIR$/003" isTestSource="false" />
       <sourceFolder url="file://$MODULE_DIR$/206" isTestSource="false" />
       <sourceFolder url="file://$MODULE_DIR$/147" isTestSource="false" />
+      <sourceFolder url="file://$MODULE_DIR$/155" isTestSource="false" />
     </content>
     <orderEntry type="inheritedJdk" />
     <orderEntry type="sourceFolder" forTests="false" />