update Algorithm-DataStructure/README.md

Author: caizkun

Algorithm-DataStructure/README.md

@@ -1,6 +1,6 @@
 ## Tips in Algorithms & Data Structures
 
-Note that in this folder each file is more like a document mixed with code. :)
+Note that in this folder each file is more like a document mixed with code. Ignore the .cpp extension. :)
 
 Below is a glimpse of some common C++ containers:
 ![C++ Containers](./CppContainerComplexity.png "C++ Containers")

Algorithm-DataStructure/general_tips.cpp

@@ -0,0 +1,66 @@
+/********************************************
+ Collections of tips learned from experience
+ *********************************************/
+
+/*
+ very useful headers
+ */
+#include <iostream>
+#include <vector>
+#include <string>
+#include <stack>
+#include <queue>
+#include <list>
+#include <unordered_map>
+#include <unordered_set>
+#include <algorithm>
+#include <cmath>
+#include <climits>
+
+// or an all-in-one trick
+//#include<bits/stdc++.h>
+
+using namespace std;
+typedef long long ll;
+
+
+// remove duplicates and keep unique items ---> sort, unique
+sort(data.begin(), data.end());     // sort first s.t. duplicates are consective
+data.resize(unique(data.begin(), data.end()) - data.begin());   // unique returns the iterator after the last unremoved item
+
+
+// lexicography order --> sort the vector of string or char
+
+
+// find the min or max of a set which keeps changing ---> heap (C++ uses priority_queue)
+priority_queue<int> max_heap(data.begin(), data.end());   // priority_queue is a max heap by defalut
+priority_queue<int, vector<int> greater<int> > min_heap(data.begin(), data.end());    // change priority_queue to a min heap;
+
+
+// type conversion/casting
+string str = to_string(123);    // num to string
+int num = stoi(str);            // string to num: stoi          needs header <string>
+int num = atoi(str.c_str());    // string to num: atoi, atoll   needs header <cstdlib>
+char c = '0' + 6;               // char of digit: c = '6'
+int i = c - 'a';                // interval between chars: if c = 'b', i = 1
+
+
+
+// dfs is feasible if the factorial(n) < 10^9, thus n < 13.
+12! ~ 10^8
+13! ~ 10^9
+
+
+// fill 0 -> (n-1) in a vector
+vector<int> v(n);
+iota(v.begin(), v.end(), 0);    // 0 is the starting value
+
+
+// number base conversion
+vector<int> digits;
+for (int m = n; m != 0; m /= 10) {
+    digits.push_back(m % 10);
+}
+
+
+