add new solutions

solutions/7/q724/solution.go

@@ -0,0 +1,21 @@
+package q724
+
+func pivotIndex(nums []int) int {
+	sumL, sumR := 0, 0
+	for _, n := range nums {
+		sumR += n
+	}
+
+	for i := range nums {
+		sumR -= nums[i]
+		if i > 0 {
+			sumL += nums[i-1]
+		}
+		if sumL == sumR {
+			return i
+		}
+	}
+	return -1
+}
+
+var _ = pivotIndex