前置知识：前缀累加和

前置知识：前缀累加和

arr[   i ....j  ]   

求sum[ i, j ]的和 等价于 sum[ i, j ] = preSum[ 0, j ] - preSum[ 0, i-1 ]

前缀和的生成：

index      0  1  2  3  4   5  6

　　arr [-3, 1, 2, 4, 0, -1, 5]   遍历arr数组一遍preSum数组就能生成好

preSum[-3, -2, 0, 4, 4, 3, 8]

 1 package class05;
 2 
 3 public class PreSum {
 4     
 5     public static long[]  PreSum(int[] nums) {
 6         if (nums == null || nums.length == 0) {
 7             return null;
 8         }
 9         long[] sum = new long[nums.length];
10         sum[0] = nums[0];
11         for (int i = 1; i < nums.length; i++) {
12             sum[i] = sum[i - 1] + nums[i];
13         }
14         return sum;
15     }
16     
17     public static void main(String[] args) {
18         int[] arr = {-3, 1, 2, 4, 0,-1,5};
19         long[] temp = PreSum(arr);
20         for(int i=0; i<temp.length; i++) {
21             System.out.println(temp[i]);
22         }
23     }
24 
25 }

标签：arr,前缀,nums,int,sum,前置,long,累加,preSum
来源： https://www.cnblogs.com/yzmarcus/p/16294426.html