数据结构与算法之数组（1）——in dart

import 'dart:math' show Random;

List<int> _array;
final _rnd = Random();
final _capacity = 100;
final _max = 100;
var _length = 0;

void main() {
  _array = List<int>(_capacity);
  // _array = List<int>.filled(_capacity, -1);

  _insert();
  _display();

  var key = _rnd.nextInt(_max);
  print('the find key is: $key');
  var pos = _find(key);
  if (pos < 0) {
    print('can not find the key: $key.
');
  } else {
    print('found the key at: $pos.
');
  }

  var oldValue = _modify(_length ~/ 2, _rnd.nextInt(_max));
  if (oldValue != null) {
    print('has modified! and oldValue is $oldValue.
');
  }
  _display();

  _delete(_rnd.nextInt(_max));
  _display();
}

void _insert() {
  for (var i = 0; i < _capacity ~/ 2; i++) {
    _array[i] = _rnd.nextInt(_max);
    _length++;
  }
}

void _display() {
  var sb = StringBuffer();
  for (var i = 0; i < _length; i++) {
    sb.write('${_array[i]}, ');
  }
  var s = sb.isEmpty ? '' : sb.toString().substring(0, sb.length - 2);
  print('$s
');
}

int _find(int key) {
  var index = -1;
  for (var i = 0; i < _length; i++) {
    if (_array[i] == key) {
      index = i;
      break;
    }
  }
  return index;
}

int _modify(int pos, int newValue) {
  int oldValue;
  if (pos > _length - 1) {
    print('out of bound!
');
  } else {
    print(
        'will modify the value(${_array[pos]}) of array[$pos] to new value: $newValue');
    oldValue = _array[pos];
    _array[pos] = newValue;
  }
  return oldValue;
}

void _delete(int key) {
  print('the deleted key is: $key');
  var pos = _find(key);
  if (pos < 0) {
    print('can not find the key: $key!
');
  } else {
    print('the index of deleted key is: $pos
');
    for (var i = pos; i < _length - 1; i++) {
      _array[i] = _array[i + 1];
    }
    _length--;
  }
}

这是用dart语言实现的数组，因为dart内置List，且面向对象，本代码故意没有使用类和内置的List的部分特性。为了保证运行效果，采用随机数进行增删改查。