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#2145 - Count the Hidden Sequences
Problem Description
You are given a 0-indexed array of n integers differences, which describes the differences between each pair of consecutive integers of a hidden sequence of length (n + 1). More formally, call the hidden sequence hidden, then we have that differences[i] = hidden[i + 1] - hidden[i].
You are further given two integers lower and upper that describe the inclusive range of values [lower, upper] that the hidden sequence can contain.
- For example, given differences = [1, -3, 4], lower = 1, upper = 6, the hidden sequence is a sequence of length 4 whose elements are in between 1 and 6 (inclusive).
- [3, 4, 1, 5] and [4, 5, 2, 6] are possible hidden sequences.
- [5, 6, 3, 7] is not possible since it contains an element greater than 6.
- [1, 2, 3, 4] is not possible since the differences are not correct.
Return the number of possible hidden sequences there are. If there are no possible sequences, return 0.
Solution
/**
* @param {number[]} differences
* @param {number} lower
* @param {number} upper
* @return {number}
*/
var numberOfArrays = function(differences, lower, upper) {
let minValue = 0;
let maxValue = 0;
let current = 0;
for (const diff of differences) {
current += diff;
minValue = Math.min(minValue, current);
maxValue = Math.max(maxValue, current);
}
const range = upper - lower;
const validRange = range - (maxValue - minValue);
return validRange >= 0 ? validRange + 1 : 0;
};