Implement floyd-warshall algorithm for course 4 assignment 1

src/floyd_warshall.rs

@@ -0,0 +1,77 @@
+use std::cmp::min;
+
+#[derive(Debug)]
+pub struct Graph {
+    pub n_nodes: usize,
+    pub n_edges: usize,
+    pub nodes: Vec<Node>,
+}
+
+#[derive(Debug)]
+pub struct Node {
+    pub id: usize,
+    pub edges: Vec<Edge>,
+}
+
+#[derive(Debug)]
+pub struct Edge {
+    pub source: usize,
+    pub target: usize,
+    pub length: i64,
+}
+
+pub fn floyd_warshall(g: Graph) -> Option<i64> {
+	let n = g.n_nodes;
+    let mut a: Vec<Vec<i64>> = vec![vec![std::i64::MAX; n]; n];
+
+    // nodes have lengths of 0 to themself
+    for i in 0..n {
+    	a[i][i] = 0;
+    }
+
+    // nodes that are connected get the length of their edge
+    for n in &g.nodes {
+    	for e in &n.edges {
+    		a[e.source][e.target] = e.length;
+    	}
+    }
+
+    // main workloop
+    for k in 0..n {
+    	let mut new_a = a.to_vec();
+    	for i in 0..n {
+    		for j in 0..n {
+    			let case_1 = a[i][j];
+    			let case_2 = match a[i][k].checked_add(a[k][j]) {
+    				Some(v) => v,
+    				None => std::i64::MAX,
+    			};
+
+    			new_a[i][j] = min(case_1, case_2);
+    		}
+    	} 
+    	a = new_a;
+    }
+
+    // node to itself is negative means we have negative cost cycles
+    for i in 0..n {
+    	if a[i][i] < 0 {
+    		return None;
+    	}
+    }
+
+    // find min path from v to u
+    let mut r = std::i64::MAX;
+    for i in 0..n {
+    	for j in 0..n {
+    		if i != j {
+	    		let d = a[i][j];
+	    		if d < r {
+	    			r = d;
+	    		}
+    		}
+    	}
+    }
+
+    Some(r)
+}