Assume you have an array of numbers, where each value occurs at most twice. We consider sums of contiguous numbers in the array. But we only consider such sums whose two endpoints have the same value. The sum includes the two equal values themselves. So if the two equal numbers are at index i and index j(i < j) in array A, then we sum all the values A[i], A[i 1], . . . , A[j].