1893. Check if All the Integers in a Range Are Covered

First, a walk-through of the code, and then an explanation.

A Walk Through Of the Solution:

  • We can sort ranges by the ranges left value (I think of ranges as ranges = [][]int{ []int{left, right} }).
  • Then I loop through ranges and:
    • If the ranges left value is greater than left, we can return false.
    • If the ranges left value is smaller than or equal to left and the ranges right is smaller than right, we can re-make left.
    • If the ranges left value is smaller than or equal to left and the ranges right is greater than or equal to right we can return true.
  • Otherwise, return false.

How This Solution Works:

I will show a couple of images to explain how this solution works.

This image shows the first part

if r[0] > left {
	return false
}

as you can see, part A in this image has the smallest left value, but since it is greater than left, we know that there will always be a range that is not covered.

This image show the second part:

if r[1] < right {
	left = r[1] + 1
}

We only have one range for this example . We can compare the ranges right and left to re-make left (The red. is the new line from left to right)

This image shows:

else {
	return true
}

The ranges left is smaller than left and the ranges right is greater than right, so we can return true.

Then at the end, we can return false because if the code has gone that far, the ranges haven’t fully covered left to right.

The Code:

func isCovered(ranges [][]int, left int, right int) bool {
    sort.Slice(ranges, func(i, j int) bool {
        return ranges[i][0] < ranges[j][0]
    })
    
    for _, r := range ranges {
        if r[0] > left {
            return false
        } else if r[1] + 1 > left {
            if r[1] < right {
                left = r[1] + 1
            } else {
                return true
            }
        }
        
    }
    
    return false
}