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MaxSubarraySumFinder.java
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MaxSubarraySumFinder.java
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import java.util.*;
/**
* *Kadane's Algorithm*
* Find the contiguous subarray within an array (containing at least one number) which has the largest sum.
* For example, given the array [-2,1,-3,4,-1,2,1,-5,4],
* the contiguous subarray [4,-1,2,1] has the largest sum = 6.
*
* @see https://leetcode.com/problems/maximum-subarray/
* @see https://discuss.leetcode.com/category/61/maximum-subarray
* @see https://www.youtube.com/results?search_query=kadane%27s+algorithm
* @see https://en.wikipedia.org/wiki/Maximum_subarray_problem
*/
public class MaxSubarraySumFinder {
public static int findMaxSubarraySum(int[] array) {
// @todo validate input for empty and null
int curMax = array[0];
int overallMax = array[0];
// We can't use an 'enhanced' for loop b/c we need to start at the 2nd index
for (int i = 1; i<array.length; i++) {
curMax = Math.max(array[i], array[i]+curMax);
overallMax = Math.max(curMax, overallMax);
}
return overallMax;
}
public static void main(String[] args) {
int result;
int testCase1[] = {-2,1,-3,4,-1,2,1,-5,4};
result = findMaxSubarraySum(testCase1);
System.out.println("testCase<"+Arrays.toString(testCase1)+"> result<"+result+">");
int testCase2[] = {-2};
result = findMaxSubarraySum(testCase2);
System.out.println("testCase<"+Arrays.toString(testCase2)+"> result<"+result+">");
int testCase3[] = {0,0};
result = findMaxSubarraySum(testCase3);
System.out.println("testCase<"+Arrays.toString(testCase3)+"> result<"+result+">");
}
}
/* A Walk Thru an Example:
LOGIC:
curMax = array[0];
overallMax = array[0];
for (int i = 1; i<array.length; i++)
curMax = Math.max(array[i], array[i]+curMax);
overallMax = Math.max(curMax, overallMax);
[-2,1,-3,4,-1,2,1,-5,4]
array[i] array[i]+curMax curMax overallMax
INIT: -2 -2
LOOP: 1 -1 1 1
-3 -2 -2 1
4 2 4 4
-1 3 3 4
2 5 5 5
1 6 6 6
-5 1 1 6
4 5 5 6
*/