Mean Squared Error

题面

实现均方误差（MSE）计算：对等长 predictions 与 targets，计算 MSE = (1/N) Σ (pred_i - targ_i)^2。

Implementation Requirements

• External libraries are not permitted.
• The solve function signature must remain unchanged.
• The final result must be stored in the mse 变量。

Examples

predictions = [1.0, 2.0, 3.0, 4.0], targets = [1.5, 2.5, 3.5, 4.5] → mse = 0.25
predictions = [10.0, 20.0, 30.0], targets = [12.0, 18.0, 33.0] → mse = 5.67

Constraints

• 1 ≤ N ≤ 100,000,000
• -1000.0 ≤ predictions[i], targets[i] ≤ 1000.0
• Performance is measured with N = 50,000,000