function trapWater(heights: number[]): number {
  let l_index = 0
  let r_index = heights.length-1
  let max_l   = 0
  let max_r   = 0
  let acc     = 0
  while(l_index<r_index){
    max_l = Math.max(max_l,heights[l_index])
    max_r = Math.max(max_r,heights[r_index])
    if(heights[l_index]>=heights[r_index]){
      r_index-=1
      if(max_r>heights[r_index] && max_l>heights[r_index]){
        acc+=Math.min(max_l,max_r)-heights[r_index]
      }
    }else if(heights[l_index]<heights[r_index]){
      l_index+=1
      if(max_r>heights[l_index] && max_l>heights[l_index]){
        acc+=Math.min(max_l,max_r)-heights[l_index]
      }
    }
  }
  return acc
}

// No modificar: necesario para evaluar el resultado.
export { trapWater };