Method build_add

code/chapter07/binary_heap.rs:59–63

切片数据逐个加入堆

(&mut self, arr: &[i32])

    // 切片数据逐个加入堆
    fn build_add(&mut self, arr: &[i32]) {
        for &val in arr {
            self.push(val);
        }
    }

    // 末尾添加一个数据，调整堆
    fn push(&mut self, val: i32) {