5-Star Review Percentage - Google Top Interview Questions

Problem Statement :

You are given a two-dimensional list of integers reviews and a positive integer threshold. Each element reviews[i] contains [x, y] meaning product i had x number of 5-star reviews and a total of y reviews. All reviews are for one store.

Return the minimum number of additional 5-star reviews we need such that the percentage of 5-star reviews in the store is at least threshold. You can assume that it's possible to reach threshold% of 5-star reviews.


1 ≤ n ≤ 100,000 where n is the length of reviews

0 ≤ threshold ≤ 100

Example 1


reviews = [
    [4, 4],
    [1, 2],
    [3, 6]

threshold = 77




So in total there were 8 5-star reviews and a total of 12 reviews. To reach 77% 5-star reviews, we need 6 
more 5-star reviews.

Example 2

reviews = [
    [10, 20]

threshold = 50




We're already at 50% 5-star reviews.

Example 3


reviews = [
    [1, 1]

threshold = 100




We're already at 100% 5-star reviews.

Solution :


                        Solution in C++ :

int solve(vector<vector<int>>& reviews, int threshold) {
    double fi = 0, xi = 0;
    for (int i = 0; i < reviews.size(); i++) {
        fi += reviews[i][1];
        xi += reviews[i][0];

    return max((double)0,
               ceil((threshold * fi - 100 * xi) / max((double)1, (100 - (double)threshold))));

                        Solution in Java :

import java.util.*;

class Solution {
    public int solve(int[][] reviews, int threshold) {
        if (threshold == 0)
            return 0;
        int totalReview = 0;
        int total5Star = 0;
        for (int i = 0; i < reviews.length; i++) {
            totalReview += reviews[i][1];
            total5Star += reviews[i][0];

        // (totalReview + x) * threshold / 100 = (total5Star + x)

        int res = (int) Math.ceil(
            (double) ((totalReview * threshold) - (100 * total5Star)) / (100 - threshold));

        return res;

                        Solution in Python : 
class Solution:
    def solve(self, reviews, threshold):
        a = 0
        b = 0
        for c, d in reviews:
            a += c
            b += d
        if a * 100 >= threshold * b:
            return 0
        delta = threshold * b - 100 * a
        return (delta + (99 - threshold)) // (100 - threshold)

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