There is a brick wall in front of you. The wall is rectangular and has several rows of bricks. The bricks have the same height but different width. You want to draw a vertical line from the **top** to the **bottom** and cross the **least** bricks.

The brick wall is represented by a list of rows. Each row is a list of integers representing the width of each brick in this row from left to right.

If your line go through the edge of a brick, then the brick is not considered as crossed. You need to find out how to draw the line to cross the least bricks and return the number of crossed bricks.

**You cannot draw a line just along one of the two vertical edges of the wall, in which case the line will obviously cross no bricks. **

**Example:**

Input:[[1,2,2,1], [3,1,2], [1,3,2], [2,4], [3,1,2], [1,3,1,1]]Output:2Explanation:

**Note:**

- The width sum of bricks in different rows are the same and won't exceed INT_MAX.
- The number of bricks in each row is in range [1,10,000]. The height of wall is in range [1,10,000]. Total number of bricks of the wall won't exceed 20,000.

```
struct Solution;
use std::collections::HashMap;
impl Solution {
fn least_bricks(wall: Vec<Vec<i32>>) -> i32 {
let n = wall.len();
let w: i32 = wall[0].iter().sum();
let mut hm: HashMap<i32, usize> = HashMap::new();
for row in wall {
let mut sum = 0;
for x in row {
sum += x;
*hm.entry(sum).or_default() += 1;
}
}
let mut max = 0;
for (k, v) in hm {
if k != w {
max = max.max(v);
}
}
(n - max) as i32
}
}
#[test]
fn test() {
let wall = vec_vec_i32![
[1, 2, 2, 1],
[3, 1, 2],
[1, 3, 2],
[2, 4],
[3, 1, 2],
[1, 3, 1, 1]
];
let res = 2;
assert_eq!(Solution::least_bricks(wall), res);
}
```