water_tapping.js

/**
 * Version 1 of water trapping function
 * @param {number[]} height array of height
 * @returns number
 */
function trapping (height) {
  let trappedWater = 0
  height.forEach((elm, i, arr) => {

    let tallLeft = elm

    for (let index = 0; index <= i; index++) {
      const element = arr[index];

      if(element> tallLeft) {
        tallLeft = element
      }
    }
    let tallRight = elm
    
    for (let index = i+1; index < arr.length; index++) {
      const element = arr[index];
      
      if(element> tallRight) {
        tallRight = element
      }
    }
    const minHeight = Math.min(tallRight, tallLeft)

    trappedWater = trappedWater + (minHeight - elm)
    
  })

  return trappedWater;
};



/**
 * Optimised water trapping function
 * @param {number[]} height array of height
 * @returns number
 */
function trappingV2 (height = []) {
  let trappedWater = 0
  height.forEach((elm, i,) => {
    trappedWater = trappedWater + waterTrappedPerHeight(height, i,elm)
  })

  return trappedWater;
};


function waterTrappedPerHeight (height, i,elm) {

      // split heights array into right and left array using the current index
      const leftArray = height.slice(0,i+1) // create a left array with current height included
      let tallLeft = Math.max(...leftArray) // find the max
  
      const rightArray = height.slice(i) // create a right array with current height included
      let tallRight = Math.max(...rightArray) // find the max
  
  
      const minHeight = Math.min(tallRight, tallLeft)

      return (minHeight - elm)
}