add

5.leetcode/src/com/fanxb/common/Q930.java

@@ -0,0 +1,38 @@
+package com.fanxb.common;
+
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.LinkedList;
+import java.util.Map;
+
+/**
+ * Created with IntelliJ IDEA
+ *
+ * @author fanxb
+ * Date: 2020/6/11 10:58
+ */
+public class Q930 {
+    public int numSubarraysWithSum(int[] nums, int goal) {
+        //计算前缀和
+        int[] sumArr = new int[nums.length];
+        sumArr[0] = nums[0];
+        for (int i = 1; i < nums.length; i++) {
+            sumArr[i] = sumArr[i - 1] + nums[i];
+        }
+        //记录前缀和的次数
+        Map<Integer, Integer> resultMap = new HashMap<>();
+        //适配第一个数就是target的情况
+        resultMap.put(0, 1);
+        int res = 0;
+        for (int i = 0; i < nums.length; i++) {
+            int r = sumArr[i], l = r- goal;
+            res += resultMap.getOrDefault(l, 0);
+            resultMap.put(r, resultMap.getOrDefault(r, 0) + 1);
+        }
+        return res;
+    }
+
+    public static void main(String[] args) {
+        System.out.println(new Q930().numSubarraysWithSum(new int[]{1, 0, 1, 0, 1}, 2));
+    }
+}