# [Facebook] Scheduling Jobs With Max Cost

### Question

Given a set of n jobs with [start time, end time, cost], find a subset so that no 2 jobs overlap and the cost is maximum.

Let’s assume the input is already sorted by start_time.

### Solution

Somebody mentioned Interval Graph, so check it out if you interested!

I am going to discuss both DP and recursive solution.

This question reminds me of [Question] 0-1 Knapsack Problem and [Question] Coin Change Problem, cuz the basic idea is to compare 2 conditions:

1. include current element
2. or, not include current element

A very good DP solution is presented in here. The code below is written by me and it’s very intuitive to read.

Leave me a comment if you have questions. And one more thing~ Happy new year!

### Code

Dp

``````private int dpSolution(Job[] jobs, int size) {
int[] dp = new int[size];
dp[size - 1] = jobs[size - 1].cost;
// cost of last job equals to just itself
for (int k = size - 2; k >= 0; k--) {
int next = findNextJob(jobs, k);
int includeK = jobs[k].cost;
if (next < size) {
includeK += dp[next];
}
int excludeK = dp[k + 1];
dp[k] = Math.max(includeK, excludeK);
}
return dp[0];
}

private int findNextJob(Job[] jobs, int k) {
int finishTime = jobs[k].finish;
int next = k + 1;
while (next < jobs.length) {
if (jobs[next].start < finishTime) {
next++;
} else {
break;
}
}
return next;
}
``````

Recursion

``````public int recursiveSolution(Job[] jobs, int size, int k) {
// max cost from (k)th job and onwards
if (k == size) {
return 0;
}
// (k)th job must not conflict with any previous job
int next = findNextJob(jobs, k);
int includeK = jobs[k].cost + recursiveSolution(jobs, size, next);
int excludeK = recursiveSolution(jobs, size, k + 1);
return Math.max(includeK, excludeK);
}

private int findNextJob(Job[] jobs, int k) {
int finishTime = jobs[k].finish;
int next = k + 1;
while (next < jobs.length) {
if (jobs[next].start < finishTime) {
next++;
} else {
break;
}
}
return next;
}
``````