Plant trees on a line segment (at both ends), and then:

Interval = number of trees planted-1

Number of trees planted = number of intervals+1

Improve the concept:

First, the problem of planting trees online can be divided into the following three situations.

1. If trees are planted at both ends of the tree planting route, the number of trees planted should be more than the interval number 1, that is, the number of trees planted = interval number+1.

2. If only one end of the tree planting line is planted with trees, then the number of trees is equal to the number of intervals to be divided, that is, the number of trees = the number of intervals.

3. If no trees are planted at both ends of the tree planting route, the number of trees planted is less than the number of intervals 1, that is, the number of trees planted = the number of intervals-1.

Second, if trees are planted around a circle, then: