leetcode-grind/problems/122/main.c

#include <stdio.h>
#include <limits.h>

int maxProfit(int*, int);
int maxProfit(int* prices, int pricesSize){
    // Each time the direction changes buy/sell at that price if possible
    // only make decision once past the decision point
    // Only count profit once sold
    int profit = 0;
    int buy = 0; // zero will represent looking to buy, 1 will be looking to sell
    int current_stock = -1; // This will represent the value of the current bought stock, to sell, put this into profit var
    int last = INT_MAX; // This will be used to look back

    // Apply basic strategy
    for (int i = 0; i < pricesSize; i++) {
        if (buy == 0 && prices[i] > last) {
            buy = 1; // buy this stuff
            current_stock = last;
        } else if (buy == 1 && prices[i] < last) {
            // sell at the last price in retrospect
            buy = 0;
            profit = profit + last - current_stock;
            current_stock = -1;
        }
        last = prices[i];
    }

    // Need to check if we can sell at last price or not
    // i.e. there hasn't been a swing back, it's all up baby
    if (current_stock != -1 && last > current_stock) {
        profit = profit + last - current_stock;
    }

    return profit; 
}

int main() {
    int prices[6] = {7, 1, 5, 3, 6, 4};
    printf("Expected: 7\n");
    printf("Got: %d\n", maxProfit(prices, 6));
    /*
    int prices_two[5] = {1, 2, 3, 4, 5};
    printf("Expected: 4\n");
    printf("Got: %d\n", maxProfit(prices_two, 5));
    int prices_three[5] = {7, 6, 4, 3, 1};
    printf("Expected: 0\n");
    printf("Got: %d\n", maxProfit(prices_three, 5));
    */
    return 0;
}