Author: Shiva Charan Devabhaktuni

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Dropdown ES6

<html>

  <head>
    <style>
      .dropdown {
        position: relative;
        display: inline-block;
      }

      .dropdown-container {
        display: none;
        position: absolute;
        width: 150px;
        border: 1px solid #000;
      }

      .show {
        display: block;
      }

    </style>
    <script>
      const toggle = (e) => {
        document.getElementById('req')
        .classList.toggle('show');
        e.stopPropagation();
      };

      const bodyHandle = (e) => {
        if (document.getElementById('req')
          .classList.contains('show')) {
          document.getElementById('req')
            .classList.toggle('show');
        }
      };

    </script>
  </head>

  <div onclick="bodyHandle(event)"
       style="width: 100vw;
              height: 100vh;
              background-color: lightgreen;">
    <div class="dropdown" onclick="toggle(event)"
         style="background-color: skyblue;">
      <button id="button">Click</button>
      <div id="req" class="dropdown-container"
           style="background-color: lightyellow;">
        <div>item 1</div>
        <div>item 2</div>
        <div>item 3</div>
      </div>
    </div>
  </div>
  </body>

</html>

Demo

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Shifting Letters – Java O(n)

class Solution {
    public String shiftingLetters(String S, int[] shifts) {
        int n = shifts.length;
        int prev = 0;
        char[] arr = S.toCharArray();
        for (int i = n - 1; i >= 0; i--) {
            prev += shifts[i] % 26;
            arr[i] = getNextChar(arr[i], prev);
        }
        return new String(arr);
    }

    public char getNextChar(char a, int diff) {
        return (char)((((a - 'a') + diff) % 26) + 'a');
    }
}
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Drag Drop ES6

The following code demonstrates drag drop functionality in ES6.

<script>
  const onDrop = (e) => {
    e.preventDefault();
 e.target.appendChild(document.getElementById(e.dataTransfer.getData('target')));
  };
  const onDragOver = (e) => e.preventDefault();
  const onDragStart = (e) => e.dataTransfer.setData('target', e.target.id);
  
</script>
<div id="dest" ondrop="onDrop(event)" ondragover="onDragOver(event)" style="height: 200px; width: 200px; border: 1px solid #000; padding: 10px; box-sizing: border-box;"></div>
<img id="source" draggable="true" ondragstart="onDragStart(event)" src="http://via.placeholder.com/180x180" />

Demo

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Loader ES6

The following is the implementation of a simple Javascript (ES6) loader.

<script>
  const load = () => {
    let width = 0;
    const id = setInterval(() => {
      if (width === 100)
        clearInterval(id);
      else
        document.getElementById('bar').style.width = `${++width}%`;
    }, 10);
  };
</script>
<div id="loader" style="height: 100px; width: 600px; border: 1px solid #000;">
  <div id="bar" style="background-color: green; width: 0; height: 100px;" class="">
  </div>
</div>
<button onclick="load()">Load</button>

Demo

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Add Events ES6

In the example below, we create a button and attach a click event to it.

const button = document.createElement('button');
 button.innerHTML = 'Click';
 document.body.appendChild(button);
 const test = (val) => {
   console.log('clicked ' + val);
 };
 button.addEventListener('click', test.bind(this, 'test'));

Demo

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Debounce (ES6)

Sometimes, we would like to wait a certain minimum time period before successive method calls. For example in events like onscroll(), onresize(), this can go a long way in terms of optimizing the page performance as a whole.

The wrapping of the methods using a Debounce method is a simple way to achieve the desired result.

const debounce = (fn, interval) => {
  let timeout;
  return (...rest) => {
    if (timeout)
      clearTimeout(timeout);
      timeout = setTimeout(() => {
        fn.apply(this, rest);
      }, interval);
  };
}

const test = (inp) => {
  console.log(inp);
};

const db = debounce(test, 1000);
const cb = () => {
  db('test');
};
const button = document.createElement('button');
button.innerHTML = 'fire';
document.body.appendChild(button);
button.addEventListener('click', cb);

Demo

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Minimum Window Substring – Java

The brute force method would be calculate all the substrings, which would be inefficient.

Runtime Complexity O(m + n)

Space Complexity O(m+n)

class Solution {
    public String minWindow(String s, String t) {
        int tLen = t.length();
        int sLen = s.length();
        if (tLen > sLen)
            return "";
        int[] pattern = new int[256];
        int[] given = new int[256];
        for (int i = 0; i < tLen; i++)
            pattern[t.charAt(i)]++;
        int mstart = 0, size = 0, start = 0, min = sLen + 1;
        for (int j = 0; j < s.length(); j++) {
            char curr = s.charAt(j);
            if (given[curr] < pattern[curr])
                size++;
            given[curr]++;
            if (size == tLen) {
                while (given[s.charAt(start)] > pattern[s.charAt(start)]) {
                    given[s.charAt(start)]--;
                    start++;
                }
                int len = j - start + 1;
                if (len < min) {
                    min = len;
                    mstart = start;
                }
            }
        }
        if (size < tLen)
            return "";
        return s.substring(mstart, mstart + min);
    }
}
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UTF-8 Validation – Java

Hint UTF-8 ranges between 1 to 4 bytes (8-bits).

Runtime: O(n)

class Solution {
    public boolean validUtf8(int[] data) {
        int n = data.length;
        int skip = 0b10000000;
        int check = 0;
        for (int currByte: data) {
            if (check > 0) {
                if ((currByte & skip) == skip)
                    check--;
                else
                    return false;
            } else {
                check = getHeadType(currByte);
                if (check < 0) return false;
            }
        }
        return check == 0;
    }

    public int getHeadType(int num) {
        if ((num & 0b11110000) == 0b11110000 && (num & 0b00001000) != 0b00001000) return 3;
        if ((num & 0b11100000) == 0b11100000 && (num & 0b00010000) != 0b00010000) return 2;
        if ((num & 0b11000000) == 0b11000000 && (num & 0b00100000) != 0b00100000) return 1;
        if ((num & 0b10000000) == 0b10000000) return -1; //error
        return 0;
    }
}

 

 

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K Empty Slots – Java

Time O(nlogn)
Space O(n)

class Solution {
    public int kEmptySlots(int[] flowers, int k) {
        if (flowers.length == 1 && k == 0) return 1;
        TreeSet < Integer > set = new TreeSet < Integer > ();
        for (int i = 0; i < flowers.length; i++) {
            int curr = flowers[i];
            Integer higher = set.higher(curr);
            if (higher != null && higher - curr == k + 1) {
                return i + 1;
            }
            Integer lower = set.lower(curr);
            if (lower != null && curr - lower == k + 1) {
                return i + 1;
            }
            set.add(curr);
        }
        return -1;
    }
}
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Top K Frequent Elements – Java

Runtime O(nlogn)

class Solution {
    public List<Integer> topKFrequent(int[] nums, int k) {
        HashMap<Integer, Integer> times = new HashMap<Integer, Integer>();
        for(int i=0; i<nums.length; i++) {
            if(times.get(nums[i])!=null) {
                times.put(nums[i], times.get(nums[i])+1);
            } else {
                 times.put(nums[i], 1);
            }
        }
        List<Integer> list = new ArrayList<Integer>(times.keySet());
        list.sort((a,b)->times.get(b)-times.get(a));
        return list.subList(0,k);
    }
}
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