solution.js

function solution(A) {
  //pit is made up of [startPeak, valley, endPeak]
  //set startPeak to first item in array
  let startPeak = A[0]; 
  let valley; //lowest point, the dip
  let endPeak; 
  let i = 1; 
  let deepestDepth = -1; 
  
  //find the begining of the pit (if first item in array is not)
  while(A[i] > startPeak) {
    startPeak = A[i];
    i++; 
  }
  
  //search for pits
  for (; i<A.length; i++) {
    //if a pit is found, calculate depth
    if (startPeak != null && valley != null && endPeak != null) {
      console.log([startPeak, valley, endPeak]);
      let depth = calculatePitDepth([startPeak, valley, endPeak]);
      if (depth > deepestDepth) deepestDepth = depth; 
      startPeak = endPeak; //the end of the pit is now the start of the next pit
      valley = null; 
      endPeak = null;
    }
    
    //otherwise, look for pit
    if (A[i] < startPeak && valley == null) {
      if (A[i] > A[i+1]) { //not at lowest point yet
        continue; 
      } else if (A[i] < A[i+1]) { //found the local minima
        valley = A[i]; 
      }
    }
    //if we've found the local minima, start looking for the end of the pit
    if (valley != null) {
      if (i != A.length - 1) {
        if (A[i] < A[i+1]) {
          continue; 
        } else if (A[i] > A[i+1]) {
          endPeak = A[i]; 
        }
      //check last value and see if it goes up or down
      } else {
        if (A[i] > valley) endPeak = A[i];
      }
      
    }
        
  }
  
  if (startPeak != null && valley != null && endPeak != null) {
    console.log([startPeak, valley, endPeak]);
    let depth = calculatePitDepth([startPeak, valley, endPeak]);
    if (depth > deepestDepth) deepestDepth = depth; 
  }
  
  return deepestDepth;
}

//Calculate depth of a pit: e.g., [0,-5,10] // returns 5
function calculatePitDepth(arr) {
  const a = arr[0] - arr[1]; 
  const b = arr[2] - arr[1];
  //smaller of the two distances
  return Math.min(a,b);
}