package chap04_Divide_And_Conquer;import static org.junit.Assert.*;
import java.util.Arrays;
import org.junit.Test;
/**
* 算反导论第四章 4.1 最大子数组
*
* @author xiaojintao
*
*/
public class Maximum_Subarray_Problem {
/**
* 最大子数组类 left为头部索引，right为尾部索引，sum为数组和
*
* @author xiaojintao
*
*/
protected static class MaxSubarray {
int left;
int right;
long sum;public MaxSubarray(int left, int right, long sum) {
this.left = left;
this.right = right;
this.sum = sum;
}
}/**
* 类似减治法，更快速的球最大子数组，支持全部都是负数的数组
*
* @param n
* @return
*/
static MaxSubarray findMaxSubarrayFaster(int[] n) {
long sum = Long.MIN_VALUE;
int right = 0;
int left = 0;
int negativeCounter = 0;
long tempSum = Long.MIN_VALUE;
long tempSum1 = 0;
// 考虑全是负数
for (int i = 0; i < n.length; i++) {
if (n[i] < 0) {
if (tempSum < n[i]) {
tempSum = n[i];
right = i;
}
negativeCounter += 1;
} else if (n[i] >= 0) {
left = i;
break;
}
}
if (negativeCounter == n.length) {
left = right;
return new MaxSubarray(left, right, tempSum);
} else {
for (int j = left; j < n.length; j++) {
tempSum1 += n[j];
if (tempSum1 > sum) {
sum = tempSum1;
right = j;
}
}
sum = Long.MIN_VALUE;
tempSum1 = 0;
int tempLeft = left;
for (int k = right; k >= tempLeft; k--) {
tempSum1 += n[k];
if (tempSum1 > sum) {
sum = tempSum1;
left = k;
}
}
return new MaxSubarray(left, right, sum);
}}
/**
* 更快的打印最大子数组
*
* @param n
*/
static void printMaxSubarrayFaster(int[] n) {
MaxSubarray maxSubarray = findMaxSubarrayFaster(n);
int[] result = Arrays.copyOfRange(n, maxSubarray.left,
maxSubarray.right + 1);
System.out.println("MaxSubarray is " + Arrays.toString(result) + "from"
+ maxSubarray.left + " to " + maxSubarray.right + ", Sum is "
+ maxSubarray.sum);
}
}
第四章 分治策略 4.1 最大子数组问题（自己想的，不知道是不是减治法）,布布扣,bubuko.com