⭐ problem solving

Author: sdettaran

problemSolving/algorithm.md

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+Algorithm is a process or set of rules to be followed in calculations or other problem-solving operations, especially by a computer.
+
+Almost everything you do in programming involves some kind of algorithm. It's the foundation of computer science and programming.
+
+### Problem Solving
+
+- Understand the problem
+- Explore concrete examples
+- Break it down
+- Solve/Simplify
+- Look back and refactor
+
+### Understand the problem
+
+- Can I restate the problem in my own words?
+- What are the inputs that go into the problem?
+- What are the outputs that should come from the solution to the problem?
+- Can the outputs be determined from the inputs? In other words, do I have enough information to solve the problem? (You may not be able to answer this question until you set about solving the problem. That's okay; it's still worth considering the question at this early stage.)
+- How should I label the important pieces of data that are a part of the problem?
+
+Example:
+
+Write a function which takes two numbers and returns their sum.
+
+1. Can I restate the problem in my own words?
+   - Implement addition
+2. What are the inputs that go into the problem?
+   - Integers?
+   - Floats?
+   - What about string for large numbers?
+3. What are the outputs that should come from the solution to the problem?
+    - Integers?
+    - Floats?
+    - String?
+4. Can the outputs be determined from the inputs? In other words, do I have enough information to solve the problem?
+    - Yes
+
+### Explore concrete examples
+
+Coming up with examples can help you understand the problem better.
+
+Examples also provide sanity checks that your eventual solution works how it should.
+
+- Start with simple examples
+- Progress to more complex examples
+- Explore examples with empty inputs
+- Explore examples with invalid inputs
+
+Example:
+
+Write a function which takes in a string and returns counts of each character in the string.
+
+```json
+charCount("aaaa"); // {a: 4}
+
+charCount("hello"); // {h: 1, e: 1, l: 2, o: 1}
+```
+
+Do we need to worry about case sensitivity? 
+Do we need to worry about spaces?
+Do we need to worry about characters that are not letters?
+Do we need to worry about characters that are not present in the input?
+
+### Break it down
+
+Explicitly write out the steps you need to take.
+
+This forces you to think about the code you'll write before you write it, and helps you catch any conceptual issues or misunderstandings before you dive in.
+
+Example:
+
+Write a function which takes in a string and returns counts of each character in the string.
+
+```json
+function charCount(str) {
+    // make object to return at end
+    // loop over string, for each character
+        // if the char is a number/letter AND is a key in object, add one to count
+        // if the char is a number/letter AND not in object, add it to object and set value to 1
+        // if the char is something else (space, period, etc.) don't do anything
+    // return object at end
+}
+
+charCount("hello");
+/*
+{
+    h: 1,
+    e: 1,
+    l: 2,
+    o: 1
+}
+*/
+
+charCount("Your PIN number is 1234");
+/*
+{
+    1: 1,
+    2: 1,
+    3: 1,
+    4: 1,
+    b: 1,
+    e: 1,
+    i: 2,
+    m: 1,
+    n: 2,
+    o: 1,
+    p: 1,
+    r: 2,
+    s: 1,
+    u: 2,
+    y: 1
+}
+*/
+```
+
+### Solve/Simplify
+
+If you can't solve the problem, solve a simpler problem.
+
+- Find the core difficulty in what you're trying to do
+- Temporarily ignore that difficulty
+- Write a simplified solution
+- Then incorporate that difficulty back in
+
+Example:
+
+Write a function which takes in a string and returns counts of each character in the string.
+
+```json
+function charCount(str) {
+    const obj = {};
+    for (let char of str) {
+        char = char.toLowerCase();
+        if (/[a-z0-9]/.test(char)) {
+            obj[char] = ++obj[char] || 1;
+        }
+    }
+    return obj;
+}
+```
+
+### Look back and refactor
+
+- Can you check the result?
+- Can you derive the result differently?
+- Can you understand it at a glance?
+- Can you use the result or method for some other problem?
+- Can you improve the performance of your solution?
+- Can you think of other ways to refactor?
+- How have other people solved this problem?
+
+Example:
+
+Write a function which takes in a string and returns counts of each character in the string.
+
+```json
+function charCount(str) {
+    const obj = {};
+    for (let char of str) {
+        char = char.toLowerCase();
+        if (/[a-z0-9]/.test(char)) {
+            obj[char] = ++obj[char] || 1;
+        }
+    }
+    return obj;
+}
+```