📘 Lesson · Lesson 78

Selection & Insertion Sort

Two Simple Sorts

💡 Note

Selection sort picks the smallest and places it first. Insertion sort inserts each element into its correct position.

Selection Sort

C++

int a[] = {5, 2, 8, 1}, n = 4;
for (int i = 0; i < n-1; i++) {
    int min = i;
    for (int j = i+1; j < n; j++)
        if (a[j] < a[min]) min = j;
    swap(a[i], a[min]);
}
// a = 1 2 5 8

Insertion Sort

C++

int a[] = {5, 2, 8, 1}, n = 4;
for (int i = 1; i < n; i++) {
    int key = a[i], j = i - 1;
    while (j >= 0 && a[j] > key) { a[j+1] = a[j]; j--; }
    a[j+1] = key;
}
// a = 1 2 5 8

Summary

Selection sort: repeatedly find the minimum and swap it forward.
Insertion sort: shift larger elements and insert each in place.

Two Simple Sorts

💡 Note

Selection sort picks the smallest and places it first. Insertion sort inserts each element into its correct position.

Selection Sort

C++

int a[] = {5, 2, 8, 1}, n = 4;
for (int i = 0; i < n-1; i++) {
    int min = i;
    for (int j = i+1; j < n; j++)
        if (a[j] < a[min]) min = j;
    swap(a[i], a[min]);
}
// a = 1 2 5 8

Insertion Sort

C++

int a[] = {5, 2, 8, 1}, n = 4;
for (int i = 1; i < n; i++) {
    int key = a[i], j = i - 1;
    while (j >= 0 && a[j] > key) { a[j+1] = a[j]; j--; }
    a[j+1] = key;
}
// a = 1 2 5 8

सारांश

Selection sort: repeatedly find the minimum and swap it forward.
Insertion sort: shift larger elements and insert each in place.

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