modify code on class

Author: 左程云

src/topinterviewquestions/Problem_0053_MaximumSubarray.java

@@ -2,6 +2,48 @@
 
 public class Problem_0053_MaximumSubarray {
 
+	public static int maxSum(int[] nums) {
+		int N = nums.length;
+		// dp[i] 含义：子数组必须以i结尾的时候，所有可以得到的子数组中，最大累加和是多少？
+		int[] dp = new int[N];
+		dp[0] = nums[0];
+		int max = Integer.MIN_VALUE;
+		for (int i = 1; i < N; i++) {
+			int p1 = nums[i];
+			int p2 = nums[i] + dp[i - 1];
+			dp[i] = Math.max(p1, p2);
+			max = Math.max(max, dp[i]);
+		}
+		return max;
+	}
+
+	public static int maxSumFollowUp(int[] arr) {
+		if (arr == null) {
+			return 0;
+		}
+		int N = arr.length;
+		if (N == 0) {
+			return 0;
+		}
+		if (N == 1) {
+			return arr[0];
+		}
+		if (N == 2) {
+			return Math.max(arr[0], arr[1]);
+		}
+		// N > 2
+		int[] dp = new int[N];
+		dp[0] = arr[0];
+		dp[1] = Math.max(arr[0], arr[1]);
+		for (int i = 2; i < N; i++) {
+			int p1 = arr[i];
+			int p2 = dp[i - 1];
+			int p3 = arr[i] + dp[i - 2];
+			dp[i] = Math.max(Math.max(p1, p2), p3);
+		}
+		return dp[N-1];
+	}
+
 	public static int maxSubArray(int[] nums) {
 		int cur = 0;
 		int max = Integer.MIN_VALUE;

src/topinterviewquestions/Problem_0062_UniquePaths.java

@@ -17,6 +17,7 @@ public static int uniquePaths(int m, int n) {
 		return (int)o1;
 	}
 
+	// 调用的时候，请保证初次调用时，m和n都不为0
 	public static long gcd(long m, long n) {
 		return n == 0 ? m : gcd(n, m % n);
 	}