从一个整数数组中找出总和为S的所有子集

本文将记录实现“从一个整数数组中找出总和为S的所有子集”功能的两种方法。

1. 使用Stack来实现

2. 不借助Stack来实现。

使用Stack来实现

import java.util.Stack;

public class GetAllSubsetByStack {

	/** Set a value for target sum */
	public static final int TARGET_SUM = 15;

	private Stack<Integer> stack = new Stack<Integer>();

	/** Store the sum of current elements stored in stack */
	private int sumInStack = 0;

	public void populateSubset(final int[] data, int fromIndex, int endIndex) {

		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. 15 = 4+6+5
	 */

	private void print(Stack<Integer> stack) {
		StringBuilder sb = new StringBuilder();
		sb.append(TARGET_SUM).append(" = ");
		for (Integer i : stack) {
			sb.append(i).append("+");
		}
		System.out.println(sb.deleteCharAt(sb.length() - 1).toString());
	}
}

方法调用的类：

public class Main {

	private static final int[] DATA = { 1, 3, 4, 5, 6, 2, 7, 8, 9, 10, 11, 13,
			14, 15 };

	public static void main(String[] args) {
		GetAllSubsetByStack example = new GetAllSubsetByStack();
		example.populateSubset(DATA, 0, DATA.length);
	}
}

不借助Stack来实现

import java.util.Arrays;

public class GetAllSubsets {

	/** Set a value for target sum */
	public static final int TARGET_SUM = 15;

	public void populateSubset(final int[] data, int fromIndex,
			final int[] stack, final int stacklen, final int target) {
		if (target == 0) {
			// exact match of our target. Success!
			printResult(Arrays.copyOf(stack, stacklen));
			return;
		}

		while (fromIndex < data.length && data[fromIndex] > target) {
			// take advantage of sorted data.
			// we can skip all values that are too large.
			fromIndex++;
		}

		while (fromIndex < data.length && data[fromIndex] <= target) {
			// stop looping when we run out of data, or when we overflow our
			// target.
			stack[stacklen] = data[fromIndex];
			populateSubset(data, fromIndex + 1, stack, stacklen + 1, target
					- data[fromIndex]);
			fromIndex++;
		}
	}

	private void printResult(int[] copyOf) {
		StringBuilder sb = new StringBuilder();
		sb.append(TARGET_SUM).append(" = ");
		for (Integer i : copyOf) {
			sb.append(i).append("+");
		}
		System.out.println(sb.deleteCharAt(sb.length() - 1).toString());
	}
}

方法调用的类：

public class Main {

	private static final int[] DATA = { 1, 3, 4, 5, 6, 2, 7, 8, 9, 10, 11, 13,
			14, 15 };

	public static void main(String[] args) {
		GetAllSubsets example = new GetAllSubsets();
		example.populateSubset(DATA, 0, new int[DATA.length], 0, 15);
	}
}

两种实现方法都会打印出如下的结果：

15 = 1+3+4+5+2
15 = 1+3+4+7
15 = 1+3+5+6
15 = 1+3+2+9
15 = 1+3+11
15 = 1+4+2+8
15 = 1+4+10
15 = 1+5+2+7
15 = 1+5+9
15 = 1+6+8
15 = 1+14
15 = 3+4+6+2
15 = 3+4+8
15 = 3+5+7
15 = 3+2+10
15 = 4+5+6
15 = 4+2+9
15 = 4+11
15 = 5+2+8
15 = 5+10
15 = 6+2+7
15 = 6+9
15 = 2+13
15 = 7+8
15 = 15


转载请注明出处： http://mouselearnjava.iteye.com/blog/1985360

评论

1 楼 hailongshih 2013-12-05  

算法还是有些没看懂,先Mark了再说