update 53.maximum-subarray.java

Author: marklcrns

53.maximum-subarray.java

@@ -0,0 +1,83 @@
+/*
+ * @lc app=leetcode id=53 lang=java
+ *
+ * [53] Maximum Subarray
+ *
+ * https://leetcode.com/problems/maximum-subarray/description/
+ *
+ * algorithms
+ * Easy (47.75%)
+ * Total Accepted:    1.3M
+ * Total Submissions: 2.8M
+ * Testcase Example:  '[-2,1,-3,4,-1,2,1,-5,4]'
+ *
+ * Given an integer array nums, find the contiguous subarray (containing at
+ * least one number) which has the largest sum and return its sum.
+ *
+ *
+ * Example 1:
+ *
+ *
+ * Input: nums = [-2,1,-3,4,-1,2,1,-5,4]
+ * Output: 6
+ * Explanation: [4,-1,2,1] has the largest sum = 6.
+ *
+ *
+ * Example 2:
+ *
+ *
+ * Input: nums = [1]
+ * Output: 1
+ *
+ *
+ * Example 3:
+ *
+ *
+ * Input: nums = [5,4,-1,7,8]
+ * Output: 23
+ *
+ *
+ *
+ * Constraints:
+ *
+ *
+ * 1 <= nums.length <= 3 * 10^4
+ * -10^5 <= nums[i] <= 10^5
+ *
+ *
+ *
+ * Follow up: If you have figured out the O(n) solution, try coding another
+ * solution using the divide and conquer approach, which is more subtle.
+ */
+class Solution {
+  public int maxSubArray(int[] nums) {
+    if (nums.length == 1) {
+      return nums[0];
+    }
+    int sum = nums[0];
+    int total = 0;
+    for (int i = 1 ; i < nums.length; i++){
+      total = total + nums[i];
+    }
+
+    Integer runningSum = sum;
+
+    for (int i = 1 ; i < nums.length; i++) {
+      if (sum + nums[i] < nums[i]) {
+        sum = nums[i];
+      } else {
+        sum += nums[i];
+      }
+      if(sum > runningSum) {
+        runningSum = sum;
+      }
+    }
+
+    if (runningSum > total) {
+      return runningSum;
+    }
+
+    return total;
+  }
+
+}