4.10 Implementing ArrayList AlgorithmsImplement ArrayList Al

1. Exam Points

Implement ArrayList Algorithms using selection and loop statements

determine a minimum or maximum value

compute a sum or average

determine if at least one element has a particular property

determine if all elements have a particular property

determine the number of elements having a particular property

access all consecutive pairs of elements

determine the presence or absence of duplicate elements

shift or rotate elements left or right

reverse the order of the elements

insert elements

delete elements

2. Knowledge Points

(1) Implement ArrayList Algorithms

There are standard ArrayList algorithms that utilize traversals to:
- determine a minimum or maximum value
- compute a sum or average
- determine if at least one element has a particular property
- determine if all elements have a particular property
- determine the number of elements having a particular property
- access all consecutive pairs of elements
- determine the presence or absence of duplicate elements

Example 1: compute a sum or average

ArrayList<Integer> list = new ArrayList<Integer>();
list.add(10);
list.add(20);
list.add(30);
list.add(40);

double sum = 0.0;

// 1. use a for loop
// i: index
// get(i): element
for (int i = 0; i < list.size(); i++) {
    sum += list.get(i);
}

System.out.println("sum:" + sum);

// 2. use a for-each loop: 
// x : element
sum = 0;
for (Integer x : list) {
    sum += x;
}

System.out.println("sum:" + sum);

// 3. get the average
System.out.println(sum / list.size());

Example 2: Find a minimum or maximum value

ArrayList<Integer> list = new ArrayList<Integer>();
list.add(11);
list.add(41);
list.add(12);
list.add(30);

// 1. use a for loop

int max = list.get(0); // first element or Integer.MIN_VALUE

for (int i = 0; i < list.size(); i++) {
    int x = list.get(i);
    if (x > max) {
        max = x;
    }
}

System.out.println("max:" + max);

// 2. use a for-each loop
max = list.get(0); // first element or Integer.MIN_VALUE
for (int x : list) {
    if (x > max) {
        max = x;
    }
}

System.out.println("max:" + max);

Example 3: Check if a list is in increasing order

ArrayList<Integer> list = new ArrayList<Integer>();
list.add(1);
list.add(2);
list.add(4);
list.add(3);

// Check if a list is increasing

boolean isIncreasing = true;

int prev = list.get(0);
for (int i = 1; i < list.size(); i++) {

    Integer current = list.get(i);
    
    if (current < prev) {
        isIncreasing = false;
    }
    
    prev = current;
}

System.out.println(isIncreasing);

Example 4: count consecutive pairs

ArrayList<Integer> list = new ArrayList<Integer>();
list.add(1);
list.add(2);
list.add(2);
list.add(3);
list.add(3);
list.add(3);
list.add(4);
list.add(3);

// count consecutive pairs

int count = 0;

for (int i = 0; i < list.size() - 1; i++) {
    if (list.get(i) == list.get(i + 1)) {
        count++;
    }
}

System.out.println(count);

4.10 Implementing ArrayList Algorithms

1. Exam Points

2. Knowledge Points

(1) Implement ArrayList Algorithms

3. Exercises