add 812 script.

Author: everthis

812-largest-triangle-area.js

@@ -0,0 +1,20 @@
+/**
+ * @param {number[][]} points
+ * @return {number}
+ */
+const largestTriangleArea = function(points) {
+    const N = points.length
+    let ans = 0
+    for(let i = 0; i < N; i++) {
+        for(let j = i + 1; j < N; j++) {
+            for(let k = j + 1; k < N; k++) {
+                ans = Math.max(ans, area(points[i], points[j], points[k]))
+            }
+        }
+    }
+    return ans
+};
+
+function area(P,Q,R) {
+    return 0.5 * Math.abs(P[0]*Q[1] + Q[0]*R[1] + R[0]*P[1] -P[1]*Q[0] - Q[1]*R[0] - R[1]*P[0])
+}