题目：

题解：

type Solution struct {
    rects [][]int
    sum   []int
}

func Constructor(rects [][]int) Solution {
    sum := make([]int, len(rects)+1)
    for i, r := range rects {
        a, b, x, y := r[0], r[1], r[2], r[3]
        sum[i+1] = sum[i] + (x-a+1)*(y-b+1)
    }
    return Solution{rects, sum}
}

func (s *Solution) Pick() []int {
    k := rand.Intn(s.sum[len(s.sum)-1])
    rectIndex := sort.SearchInts(s.sum, k+1) - 1
    r := s.rects[rectIndex]
    a, b, y := r[0], r[1], r[3]
    da := (k - s.sum[rectIndex]) / (y - b + 1)
    db := (k - s.sum[rectIndex]) % (y - b + 1)
    return []int{a + da, b + db}
}