How do I find the maximum number of all the dp[1] values? In this example below, answer is 21, as I only look at the second number of the set. Currently using a for loop, but looking for something efficient.
int[][] dp = new int[30][2];
{5,9}, {31,7}, {4, 21}, {24, 16}
This question is slightly different Java- Finding maximum number in a 2D array
This can be solved in a straightforward manner using streams:
int[][] dp = {{5,9}, {6,7}, {4, 21}, {7, 12}};
int max = Arrays.stream(dp).mapToInt(a -> a[1]).max().orElseThrow();
This streams over the outer array, maps each inner array to the second element of that array, then returns the maximum element of those mapped values.
Arrays.stream(dp) - Returns a Stream<int[]> of the array's elements.mapToInt(a -> a[1]) - Applies a ToIntFunction<int[]> to each element of the Stream<int[]>, returning an IntStream of those results. This uses function a -> a[1], which takes an array and returns the element at index 1.max() - Returns the maximum int in the IntStream as an OptionalInt. This OptionalInt will contain the max value (unless the stream is empty, in which case it'll be an empty OptionalInt).orElseThrow - Returns the int value in the OptionalInt, or throws NoSuchElementException if the OptionalInt is empty.
forloop should be super efficient, though perhaps a bit more verbose (and less potentially parallelizable) than other approaches. For instance, you're unlikely to find a solution that's more efficient thanint max = Integer.MIN_VALUE; for (int[] arr : dp) { max = Math.max(arr[1], max); }