Leetcode candy中c++解法

/**********************************************************************************
*
* There are N children standing in a line. Each child is assigned a rating value.
*
* You are giving candies to these children subjected to the following requirements:
*
* Each child must have at least one candy.
* Children with a higher rating get more candies than their neighbors.
*
* What is the minimum candies you must give?
*
*
**********************************************************************************/
此题解法很巧妙，首先将权重数组从做到又进行处理，只要大于前一个权重，则使得分配数加1
例如5, 6, 7, 4, 1, 2, 3, 2, 1, 7是一个权重数组
则  1  2  3  1  1  2  3  1  1  2
然后从右向左即可做出统计total的值

#include <stdlib.h>
#include <time.h>
#include <iostream>
#include <vector>
using namespace std;

void print(vector<int> &v);

/*
*    The soluiton is O(2n) run-time complexity
*
*    For example:
*
*        ratings[] = { 5, 6, 7, 4, 1, 2, 3, 2, 1, 7 }
*
*    1) Go through the ratings from left to right.
*
*       Find the each increasing sub-array, giving the minimal candy
*
*        ratings[] = { 5, 6, 7,   4,   1, 2, 3,   2,   1, 7 }
*                      ------>    ->   ------>    ->   --->
*          candy[] = { 1, 2, 3,   1,   1, 2, 3,   1,   1, 2 }
*
*    2) Go through the raings from right to left.
*
*             ratings[] = { 5,   6,   7, 4, 1,   2,   3, 2, 1,   7 }
*                           <-   <-   <------    <-   <------    <-
*          prev_candy[] = { 1,   2,   3, 1, 1,   2,   3, 1, 1,   2 }
*                                        +1              +1
*               candy[] = { 1,   2,   3, 2, 1,   2,   3, 2, 1,   2 }
*
*    3) total candy is 19
*
*/
int candy(vector<int> &ratings) {

vector<int> candyCnt(ratings.size()) ;
//allocate candies, considering the minimal rating on the left
candyCnt[0] = 1;
for(int i = 1; i < ratings.size(); i++){
candyCnt[i] = ratings[i] > ratings[i-1] ? candyCnt[i-1]+1 : 1;
}
print(candyCnt);
//modify the allocation, considering the minimal rating on the right
int totalCandy = candyCnt[ratings.size()-1];
for(int i = ratings.size()-2; i >= 0; i--){
candyCnt[i] = (ratings[i] > ratings[i+1] && candyCnt[i+1]+1 > candyCnt[i]) ? candyCnt[i+1]+1 : candyCnt[i];
//count total candies by the way
totalCandy += candyCnt[i];
}
print(candyCnt);
return totalCandy;
}

void generateRatings(vector<int> &ratings, int n) {
srand(time(0));
for (int i=0; i<n; i++) {
ratings.push_back(rand()%10);
}
}

void print(vector<int> &v) {
for(int i=0; i<v.size(); i++){
cout << v[i] << " ";
}
cout << endl;
}

int main(int argc, char**argv)
{
int n = 10;
if (argc>1){
n = atoi(argv[1]);
}
vector<int> ratings;
generateRatings(ratings, n);
print(ratings);

cout << candy(ratings) << endl;

cout << "--------------------" << endl;
int r[] = { 5, 6, 7, 4, 1, 2, 3, 2, 1, 7 };
vector<int> ra(r, r+sizeof(r)/sizeof(r[0]));
print(ra);
cout << candy(ra) << endl;
return 0;
}