Merge branch 'master' of https://github.com/ryohang/java-basic

Author: Yihao129

python/README.md

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+# Leetcode challenge in python
+ learn basic data structure and practice in python
+
+## data structure
+   * Queue [Link to python documentation](https://docs.python.org/3/library/queue.html)
+   * Stack
+   * List
+   * Dict(Map)
+   * Tree
+
+## algrithm highlight
+### binary tree dfs
+```python
+def preorder(root):
+    if root:
+        return [root.val] + preorder(root.left) + preorder(root.right) 
+    else:
+        return []
+```
+
+## Environment setup
+### python installation
+```bash
+    pipenv install
+    pipenv shell
+```
+

src/main/java/io/ascending/training/algorithm/BaseBallWarmUp.java

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+package io.ascending.training.algorithm;
+
+import java.util.Stack;
+
+public class BaseBallWarmUp {
+    public int calPoints(String[] ops) {
+        int sum=0;
+        Stack<Integer> history = new Stack();
+        for(String str: ops){
+            Integer currentPoint;
+            switch (str) {
+                case "+":
+                    if(history.size()>1){
+                        Integer last = history.pop();
+                        Integer lastLast = history.peek();
+                        currentPoint = last+lastLast;
+                        sum+=currentPoint;
+                        history.push(last);
+                        history.push(currentPoint);
+                    }
+                    break;
+                case "D":
+                    if(history.size()>0){
+                        Integer lastRound = history.peek();
+                        currentPoint = lastRound*2;
+                        sum+=currentPoint;
+                        history.push(currentPoint);
+                    }
+                    break;
+                case "C":
+                    if(history.size()>0){
+                        currentPoint = history.pop();
+                        sum-=currentPoint;
+                    }
+                    break;
+                default:
+                    currentPoint = Integer.valueOf(str);
+                    sum+=currentPoint;
+                    history.push(currentPoint);
+                    break;
+            }
+//            System.out.println("current round:"+sum);
+        }
+        return sum;
+    }
+    public static void main(String[] args){
+        String[] vals = {"5","-2","4","C","D","9","+","+"};
+        BaseBallWarmUp bbwp = new BaseBallWarmUp();
+        System.out.println(bbwp.calPoints(vals));
+    }
+}