68 lines
2.0 KiB
C++
68 lines
2.0 KiB
C++
// Source : https://leetcode.com/problems/calculate-money-in-leetcode-bank/
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// Author : Hao Chen
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// Date : 2021-03-28
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/*****************************************************************************************************
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*
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* Hercy wants to save money for his first car. He puts money in the Leetcode bank every day.
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*
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* He starts by putting in $1 on Monday, the first day. Every day from Tuesday to Sunday, he will put
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* in $1 more than the day before. On every subsequent Monday, he will put in $1 more than the
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* previous Monday.
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*
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* Given n, return the total amount of money he will have in the Leetcode bank at the end of the n^th
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* day.
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*
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* Example 1:
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*
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* Input: n = 4
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* Output: 10
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* Explanation: After the 4^th day, the total is 1 + 2 + 3 + 4 = 10.
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*
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* Example 2:
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*
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* Input: n = 10
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* Output: 37
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* Explanation: After the 10^th day, the total is (1 + 2 + 3 + 4 + 5 + 6 + 7) + (2 + 3 + 4) = 37.
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* Notice that on the 2^nd Monday, Hercy only puts in $2.
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*
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* Example 3:
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*
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* Input: n = 20
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* Output: 96
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* Explanation: After the 20^th day, the total is (1 + 2 + 3 + 4 + 5 + 6 + 7) + (2 + 3 + 4 + 5 + 6 + 7
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* + 8) + (3 + 4 + 5 + 6 + 7 + 8) = 96.
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*
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* Constraints:
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*
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* 1 <= n <= 1000
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******************************************************************************************************/
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class Solution {
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public:
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int totalMoney(int n) {
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int weeks = n / 7;
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int days = n % 7;
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int m = 1 + 2 + 3 + 4 + 5 + 6 + 7;
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// we know
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// week1 = 0*7 + m
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// week2 = 1*7 + m
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// week3 = 2*7 + m
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// weekn = (n-1)*7 + m
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// So,
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// week1 + week2 + week3 + ....+ weekn
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// = n*m + 7*(0+1+2+..n-1)
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// = n*m + 7*(n-1)*n/2
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int money = weeks*m + 7 * (weeks-1) * weeks / 2;
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// for the rest days
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// every day needs to add previous `weeks * 1`, it is days* weeks
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// then add from 1 to days
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money += (days*weeks + days*(days+1)/2);
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return money;
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}
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};
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