add solution of problem 53: Maximum Subarray

Author: ppulse

MaximumSubarray53/README.md

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+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`.

MaximumSubarray53/Solution.java

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+public class Solution {
+    public int maxSubArray(int[] nums) {
+        if (nums == null || nums.length == 0)
+            return 0;
+        int sum = nums[0];
+        int maxSum = sum;
+        
+        for (int i = 1; i < nums.length; i++) {
+            if (sum < 0) {
+                sum = nums[i];
+            } else {
+                sum += nums[i];
+            }
+            
+            if (maxSum < sum) {
+                maxSum = sum;
+            }
+        }
+        
+        return maxSum;
+    }
+}