Find all combinations of 3 integers between 1 and 4 that sum to 6.
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And see which == 6.
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find(int[] array, int i):
if i == array.length:
return
sum = sum of array elements up to index i (exclusive)
for guess from 1 to 4:
array[i] = guess
if i == array.length - 1 && sum + guess == 6:
print array //found one
else if guess + sum >= 6:
return //dead end
else:
find(array, i + 1) //recurse
return
find(new array[3], 0)
find(int start, int end, int total, int[] array, int i): if i == array.length: return sum = sum of array elements up to index i (exclusive) for guess from start to end: array[i] = guess if i == array.length - 1 && sum + guess == total: print array else if guess + sum >= total: return else: find(start, end, total, array, i + 1) return
find(int start, int end, int total, int[] array, int i): list = new empty list if i == array.length: return list //still empty sum = sum of array elements up to index i (exclusive) for guess from start to end: array[i] = guess if i == array.length - 1 && sum + guess == total: list.add(copy of array) else if guess + sum >= total: return list //might be empty else: sublist = find(start, end, total, array, i + 1) //recurse list.addAll(sublist) return list //might be empty
..|2. 2.|.4 ----- ..|4. 3.|..
sudoku(board, row, col):
if board.isFull:
return OK
if (row,col) already set:
return sudoku(board, next(row,col)) //on to next square
for guess 1 to 4:
board.set(row, col, guess)
if board.checkRow? and board.checkCol? and board.checkSquare?:
ok? = sudoku(board, next(row,col))
if ok?:
return OK
board.unset(row,col)
return !OK //no guess worked here
..|2. 2.|.4 ----- ..|4. 3.|..
####### # S# # # ### # # E #######
Similarities:
So parameters considered by some to be a subset of local variables.
Differences:
Once Quiz 03 closes, if you answered local variables = local + parameters, you'll get partial credit. But, in future, please consider them separately.
breakSometimes important (or just easier) to break out of a loop early:
int[] nums = {1, 5, -2, 10};
//sum all values up to first negative number
int sum = 0;
for (int i = 0; i < nums.length; i++) {
if (nums[i] >= 0) {
sum += nums[i];
}else {
break;
}
}
System.out.println("Sum of initial positives only: " + sum);
break; used here? (would get 16, not 6)
break if you use extra test or variable, though:
for (int i = 0; i < nums.length && nums[i] >= 0; i++) {
sum += nums[i];
}
if (negative == true) {
java.util.Scanner keybd = new java.util.Scanner(System.in);
int oneToTen = 0;
while (true) {
try {
System.out.print("Enter an int b/w 1 and 10: ");
oneToTen = keybd.nextInt();
if (oneToTen >= 1 && oneToTen <= 10) {
break; //good input
}else {
System.out.println("That is not between 1 and 10.");
}
}catch (java.util.InputMismatchException e) {
System.out.println("That is not a number.");
keybd.nextLine(); //clear input stream
}
}
//...use oneToTen here...
continue
break or continue other than most recent containing loop.
import java.util.ArrayList;
public class ComboSumFinder {
/** Prints all combos of 3 ints, each between 1 to 4, that add up to 6. */
public static void main(String[] args) {
ArrayList<int[]> combos = find(3, 1, 4, 6);
for (int[] combo : combos) {
System.out.println(java.util.Arrays.toString(combo));
}
}
/**
* Returns a list of all combos of the given length, formed of integers
* between start and end (both inclusive), that add up to total.
*/
public static ArrayList<int[]> find(int length, int start, int end, int total) {
return find(start, end, total, new int[length], 0);
}
private static ArrayList<int[]> find(int start, int end, int total,
int[] array, int i) {
ArrayList<int[]> list = new ArrayList<int[]>();
if (i == array.length) {
return list;
}
//sum of elements in array up to index i (exclusive)
int sum = 0;
for (int j = 0; j < i; j++) {
sum += array[j];
}
//try each value for current array element from start to end
for (int guess = start; guess <= end; guess++) {
array[i] = guess;
if (i == array.length - 1 && sum + guess == total) {
list.add(java.util.Arrays.copyOf(array, array.length));
}else if (guess + sum >= total) {
return list;
}else {
ArrayList<int[]> sublist = find(start, end, total, array, i + 1);
list.addAll(sublist);
}
}
return list;
}
}