领扣303题目解法

src/main/java/com/ximo/datastructuresinaction/leetcode/solution303/NumArray.java

@@ -0,0 +1,30 @@
+package com.ximo.datastructuresinaction.leetcode.solution303;
+
+/**
+ * @author xikl
+ * @date 2019/1/8
+ */
+public class NumArray {
+
+    /**
+     * sum[0] = 0
+     * sum[i] 等于 前i个元素的和
+     */
+    private int[] sum;
+
+    public NumArray(int[] nums) {
+        sum = new int[nums.length + 1];
+        sum[0] = 0;
+
+        for (int i = 1; i < sum.length; i++) {
+            sum[i] = sum[i - 1] + nums[i - 1];
+        }
+
+    }
+
+    public int sumRange(int i, int j) {
+        return sum[j + 1] - sum[i];
+    }
+
+
+}