Intermediate · Nested loops · 122 of 264
Pairs that add up
Count the pairs of positions (i < j) whose numbers add up to a target.
Input: whole numbers on one line, then the target on the next line. Output: the number of pairs.
Examples
Input
1 2 3 4 5 5
Output
2
Input
1 1 1 2
Output
3
Input
3 7 11
Output
0
One more test checks other inputs when you press Check.
Stuck? The idea behind nested loops
A loop inside a loop: for each turn of the outer loop, the inner one runs all the way through. Good for rows and columns.
print(..., end="") stays on the same line; an empty print() after the inner loop moves to the next row.
for row in range(1, 4):
line = []
for col in range(1, 4):
line.append(str(row * col))
print(" ".join(line))Watch for: print(x, end=" ") leaves a space at the end of every line, and the tests see it. Build each line as a list and print " ".join(line): spaces only between.