LeetCode——Maximum Subarray

LeetCode——Maximum Subarray

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.

題目： 找出整數數組中連續的和最大的那個數。

從頭開始計算，遇到有和小於0的，則忽略前面的和，往前計算。

	public static int maxSubArray(int[] A) {
		int sum = 0;
		int maxSum = Integer.MIN_VALUE;
		for (int i = 0; i < A.length; i++) {
			sum += A[i];
			if (sum < 0)
				sum = 0;
			maxSum = Math.max(maxSum, sum);
		}
		return maxSum;
	}

動態規劃的方法。

	public static int maxSubArray(int[] A) {
		int max = A[0];
		int sum[] = new int[A.length];
		sum[0] = A[0];
		for (int i = 1; i < A.length; i++) {
			sum[i] = Math.max(A[i], sum[i - 1] + A[i]);
			max = Math.max(max, sum[i]);
		}
		return max;
	}