303.NumArray-一维前缀和

Author: YimingWei

NumArray.java

@@ -0,0 +1,21 @@
+class NumArray {
+    private int[] preSum;
+
+    public NumArray(int[] nums) {
+        preSum = new int[nums.length+1];
+        preSum[0] = 0;
+        for(int i=1; i<=nums.length; i++) {
+            preSum[i] = preSum[i-1] + nums[i-1];
+        }
+    }
+    
+    public int sumRange(int left, int right) {
+        return preSum[right+1] - preSum[left];
+    }
+}
+
+/**
+ * Your NumArray object will be instantiated and called as such:
+ * NumArray obj = new NumArray(nums);
+ * int param_1 = obj.sumRange(left,right);
+ */