Add Maximum Subarray Sum

Author: marttp

kotlin/Dynamic Programming/MaximumSubarraySum.kt

@@ -0,0 +1,17 @@
+fun maximumSubarraySum(nums: List<Int>): Int {
+    if (nums.isEmpty()) {
+        return 0
+    }
+    // Set the sum variables to negative infinity to ensure negative
+    // sums can be considered.
+    var maxSum = Int.MIN_VALUE
+    var currentSum = Int.MIN_VALUE
+    // Iterate through the array to find the maximum subarray sum.
+    for (num in nums) {
+        // Either add the current number to the existing running sum, or
+        // start a new subarray at the current number.
+        currentSum = maxOf(currentSum + num, num)
+        maxSum = maxOf(maxSum, currentSum)
+    }
+    return maxSum
+}

kotlin/Dynamic Programming/MaximumSubarraySumDP.kt

@@ -0,0 +1,19 @@
+fun maximumSubarraySumDP(nums: IntArray): Int {
+    val n = nums.size
+    if (n == 0) {
+        return 0
+    }
+    val dp = IntArray(n)
+    // Base case: the maximum subarray sum of an array with just one
+    // element is that element.
+    dp[0] = nums[0]
+    var maxSum = dp[0]
+    // Populate the rest of the DP array.
+    for (i in 1 until n) {
+        // Determine the maximum subarray sum ending at the current
+        // index.
+        dp[i] = maxOf(dp[i - 1] + nums[i], nums[i])
+        maxSum = maxOf(maxSum, dp[i])
+    }
+    return maxSum
+}

kotlin/Dynamic Programming/MaximumSubarraySumDPOptimized.kt

@@ -0,0 +1,13 @@
+fun maximumSubarraySumDPOptimized(nums: IntArray): Int {
+    val n = nums.size
+    if (n == 0) {
+        return 0
+    }
+    var currentSum = nums[0]
+    var maxSum = nums[0]
+    for (i in 1 until n) {
+        currentSum = maxOf(nums[i], currentSum + nums[i])
+        maxSum = maxOf(maxSum, currentSum)
+    }
+    return maxSum
+}