# [LeetCode]#2103. Rings and Rods

**Environment: Python 3.8**

**Key technique: set, if, for**

There are `n`

rings and each ring is either red, green, or blue. The rings are distributed **across ten rods** labeled from `0`

to `9`

.

You are given a string `rings`

of length `2n`

that describes the `n`

rings that are placed onto the rods. Every two characters in `rings`

forms a **color-position pair** that is used to describe each ring where:

- The
**first**character of the`ith`

pair denotes the`ith`

ring's**color**(`'R'`

,`'G'`

,`'B'`

). - The
**second**character of the`ith`

pair denotes the**rod**that the`ith`

ring is placed on (`'0'`

to`'9'`

).

For example, `"R3G2B1"`

describes `n == 3`

rings: a red ring placed onto the rod labeled 3, a green ring placed onto the rod labeled 2, and a blue ring placed onto the rod labeled 1.

Return *the number of rods that have **all three colors** of rings on them.*

**Example 1:**

**Input:** rings = "B0B6G0R6R0R6G9"

**Output:** 1

**Explanation:**

- The rod labeled 0 holds 3 rings with all colors: red, green, and blue.

- The rod labeled 6 holds 3 rings, but it only has red and blue.

- The rod labeled 9 holds only a green ring.

Thus, the number of rods with all three colors is 1.

**Analysis:**

- Use set array
- Search each location rod its R, G, B rings as below.
- Return each set length =>3.

**Solution:**

`class Solution:`

def countPoints(self, rings: str) -> int:

rods = [set() for _ in range(10)]

ans=0

for i in range(0, len(rings), 2):

rods[int(rings[i+1])].add(rings[i])

for j in rods:

if len(j)>=3:

ans+=1

return ans

**Submissions:**

**Reference:**

https://leetcode.com/problems/rings-and-rods/discuss/1624322/Python3-array-of-sets