Author: Shiva Charan Devabhaktuni

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3Sum

Time O(n2) & Memory O(1)

class Solution {
 public List < List < Integer >> threeSum(int[] nums) {
  int n = nums.length;
  List < List < Integer >> list = new ArrayList < List < Integer >> ();
     if(nums == null || nums.length<3)
        return list;
  Arrays.sort(nums);
  int left, right;
  for (int i = 0; i < n - 2; i++) {
   if(i > 0 && nums[i] == nums[i-1])
       continue;
   left = i + 1;
   right = n - 1;
   while (left < right) {
    if (nums[left] + nums[right] + nums[i] == 0) {
     List < Integer > temp = new ArrayList < Integer > ();
     temp.add(nums[i]);
     temp.add(nums[left]);
     temp.add(nums[right]);
     list.add(temp);
     left++;
     right--;
     while (nums[left] == nums[left - 1]) {
      left++;
     }
     while (left< right && nums[right] == nums[right + 1]) {
      right--;
     }
    } else if (nums[left] + nums[right] + nums[i]  > 0) {
     right--;
    } else
     left++;
   }
  }
  return list;
 }
}

Javascript ES6

const get3Sum = (arr) => {
  const results = [];
  arr.sort((a, b) => a - b);
  for (let i = 0; (i < arr.length - 2) && (arr[i] <= 0); i++) {
    if (i === 0 || arr[i] !== arr[i - 1]) {
      getPair(arr, i, results);
    }
  }
  return results;
};

const getPair = (arr, i, results) => {
  let left = i + 1;
  let right = arr.length - 1;
  while (left < right) {
    const sum = arr[i] + arr[left] + arr[right];
    if (sum === 0) {
      results.push([arr[i], arr[left++], arr[right--]]);
      while (arr[left - 1] == arr[left]) {
        left++;
      }
    } else if (sum < 0) {
      left++;
    } else if (sum > 0) {
      right--;
    }
  }
};

console.log(get3Sum([-1, 0, 1, 2, -1, -4]));
// [[-1 , 0, 1], [-1, -1, 2]]

Demo

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Trapping Rain Water

Javascript (ES6)

/**
 * @param {number[]} height
 * @return {number}
 */
const trap = function(height) {
  const left = [];
  const right = [];
  let lmax = height[0];
  let rmax = height[height.length - 1];
  for (let i = 0; i < height.length; i++) {
    if (height[i] > lmax) {
      lmax = height[i];
    }
    left[i] = lmax;
    let j = height.length - i - 1;
    if (height[j] > rmax) {
      rmax = height[j];
    }
    right[j] = rmax;
  }
  let total = 0;
  for (let i = 0; i < height.length; i++) {
    total += Math.abs(height[i] - Math.min(left[i], right[i]));
  }
  return total;
};

console.log(trap([0, 1, 0, 2, 1, 0, 1, 3, 2, 1, 2, 1])); // 6

Demo

Java

Time: O(n)
Memory: O(n)


class Solution {
 public int trap(int[] height) {
  int n = height.length;
  if (n == 0)
   return 0;
  int[] left = new int[n];
  int[] right = new int[n];
  left[0] = height[0];
  right[n - 1] = height[n - 1];
  int j;
  for (int i = 1; i < n; i++) {
   left[i] = Math.max(left[i - 1], height[i]);
   right[n - i - 1] = Math.max(right[n - i], height[n - i - 1]);
  }
  int area = 0;
  for (int i = 1; i < n - 1; i++) {
   area += Math.min(left[i], right[i]) - height[i];
  }
  return area;
 }
}
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CSS Margins Collapsing

CSS Vertical Margins  of adjoining elements collapse vertically by default unless contained in a flexbox.

CSS Horizontal Margins never collapse.

Continue reading “CSS Margins Collapsing”
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Frog Jump – Java

This solution uses a HashMap

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Flexbox – Div at end of row

The following lines of code demonstrate how to align a div at the end of the flexbox row when you want to display the rest of the them at the start.
flexbox

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Unit testing method called with parameters

The following two unit tests demonstrate the scenario where you would want to write a unit test to verify whether a method was called with the required parameters. It also tests how many times a method was invoked by passing a mock method.

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Allow arrow functions as properties in React Components using eslint

If you don’t configure your .eslintrc file, then you might see this “Parsing error: Unexpected token =” when you do the following in your react components.

class HomeComponent extends Component {
  
  state = {
    term: '',
  };

  setTerm = (term) => {
    this.setState({ term });
  };

  ...
}

To use arrow functions as properties in React components you can do the following.

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Add Stylelint to webpack

Adding stylelint to your project has many advantages that range from being able to throw warnings and errors when the styling rules (CSS, SASS-SCSS) are broken, to being able to fix most of your warnings automatically with a single command.

Continue reading “Add Stylelint to webpack”
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How to create an arrow content separator in CSS

Lets say you want to draw something similar to the following using only CSS.

Continue reading “How to create an arrow content separator in CSS”
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Format currency and date manually in Javascript

Format Currency

In case you want to implement a function to format currency instead of just using toLocaleString() then, you can use the following.

Continue reading “Format currency and date manually in Javascript”