我想知道如何使用负值和负目标,现在我的程序在给出这些变量的负值时给出索引超出范围的错误。我需要我的hasSum函数与此项目的负值一起工作,我不能只是假设积极。
import java.util.Stack;
import java.util.Scanner;
public class subsetSum {
static Scanner input = new Scanner(System.in);
static {
System.out.print("Enter the target (T)" + "\n");
}
/** Set a value for target sum */
static int TARGET_SUM = input.nextInt(); //this is the target
/** Store the sum of current elements stored in stack */
static int sumInStack = 0;
Stack<Integer> stack = new Stack<Integer>();
public static void main(String[] args) {
//the size is S
System.out.println("\n" + "Enter the size of the set (S)");
int values = input.nextInt(); //size = "values"
//value of each size entry
System.out.println("\n" + "Enter the value of each entry for S");
int [] numbers = new int[values];
for(int i = 0; i < values; i++) //for reading array
{
numbers[i] = input.nextInt();
}
if(hasSum(numbers, TARGET_SUM)){
System.out.println("\n" + "Can: ");
subsetSum get = new subsetSum(); // encapsulation
get.populateSubset(numbers, 0, numbers.length);
}else{
System.out.println("\n" + "Cannot");
}
}
//method based on dynamic programming O(sum*length)
public static boolean hasSum(int [] array, int sum)
{
int i;
int len = array.length;
boolean[][] table = new boolean[sum + 1][len + 1]; //this has to be changed for negative
//If sum is zero; empty subset always has a sum 0; hence true
for(i = 0; i <= len; i++){
table[0][i] = true;
}
//If set is empty; no way to find the subset with non zero sum; hence false
for(i = 1; i <= sum; i++){
table[i][0] = false;
}
//calculate the table entries in terms of previous values
for(i = 1; i <= sum; i++)
{
for(int j = 1; j <= len; j++)
{
table[i][j] = table[i][j - 1];
if(!table[i][j] && i >= array[j - 1]){
table[i][j] = table[i - array[j - 1]][j - 1];
}
}
}
return table[sum][len]; //this has to be changed for negative
}
public void populateSubset(int[] data, int fromIndex, int endIndex) {
/*
* Check if sum of elements stored in Stack is equal to the expected
* target sum.
*
* If so, call print method to print the candidate satisfied result.
*/
if (sumInStack >= TARGET_SUM) {
if (sumInStack == TARGET_SUM) {
print(stack);
}
// there is no need to continue when we have an answer
// because nothing we add from here on in will make it
// add to anything less than what we have...
return;
}
for (int currentIndex = fromIndex; currentIndex < endIndex; currentIndex++) {
if (sumInStack + data[currentIndex] <= TARGET_SUM) {
stack.push(data[currentIndex]);
sumInStack += data[currentIndex];
/*
* Make the currentIndex +1, and then use recursion to proceed
* further.
*/
populateSubset(data, currentIndex + 1, endIndex);
sumInStack -= (Integer) stack.pop();
}
}
}
/**
* Print satisfied result. i.e. 5 = 1, 4
*/
private void print(Stack<Integer> stack) {
StringBuilder sb = new StringBuilder();
for (Integer i : stack) {
sb.append(i).append(",");
}
// .deleteCharAt(sb.length() - 1)
System.out.println(sb.deleteCharAt(sb.length() - 1).toString());
}
}
答案 0 :(得分:1)
您是要查找子集或子阵列的总和吗? 如果是子集,那么简单的递归就可以解决这个问题,例如:
public static boolean hasSum(int [] array, int sum)
{
return hasSum(array, 0, 0, sum);
}
private static boolean hasSum(int[] array, int index, int currentSum, int targetSum) {
if (currentSum == targetSum)
return true;
if (index == array.length)
return false;
return hasSum(array, index + 1, currentSum + array[index], targetSum) || // this recursion branch includes current element
hasSum(array, index + 1, currentSum, targetSum); // this doesn't
}
如果您要查找子阵列,我会使用prefix sums,例如:
public static boolean hasSum(int [] array, int sum)
{
int[] prefixSums = new int[array.length];
for (int i = 0; i < prefixSums.length; i++) {
prefixSums[i] = (i == 0) ? array[i] : array[i] + prefixSums[i - 1];
}
for (int to = 0; to < prefixSums.length; to++) {
if (prefixSums[to] == sum)
return true; // interval [0 .. to]
for (int from = 0; from < to; from++) {
if (prefixSums[to] - prefixSums[from] == sum)
return true; // interval (from .. to]
}
}
return false;
}
BTW我认为在静态初始值设定项中读取Scanner
的输入值是一个坏主意,为什么不将它们移到main()
?