From 9970586deb17a5e8623619d79245fa4c7a5d9b55 Mon Sep 17 00:00:00 2001
From: tomsmeding <tom.smeding@gmail.com>
Date: Wed, 22 Mar 2017 20:55:25 +0100
Subject: FIX CRITICAL BUG: timing issue where simulation was subtly incorrect

---
 world.cpp | 53 ++++++++++++++++++++++++++++++++---------------------
 1 file changed, 32 insertions(+), 21 deletions(-)

diff --git a/world.cpp b/world.cpp
index ff13d46..f71eefe 100644
--- a/world.cpp
+++ b/world.cpp
@@ -1,7 +1,8 @@
+#include <unordered_map>
+#include <utility>
 #include <cstdlib>
 #include <cassert>
 #include <cstring>
-#include <unordered_map>
 
 #include "world.h"
 
@@ -301,29 +302,39 @@ void World::removeTeam(const Team *team){
 }
 
 void World::tick(){
+	vector<pair<int,int>> candidates;
+	candidates.reserve(SIZE*SIZE);
+
 	for(int y=0;y<SIZE;y++){
 		for(int x=0;x<SIZE;x++){
-			if(!board[y][x])continue;
-			switch(board[y][x]->tick(*this)){
-				case WorldAction::none: break;
-
-				case WorldAction::die:
-					delete board[y][x];
-					board[y][x]=nullptr;
-					break;
-
-				case WorldAction::move:{
-					Robot** ptr=nullptr;
-					switch(board[y][x]->heading%4){
-						case 0: ptr=&board[(y+SIZE-1)%SIZE][x]; break;
-						case 1: ptr=&board[y][(x+1)%SIZE]; break;
-						case 2: ptr=&board[(y+1)%SIZE][x]; break;
-						case 3: ptr=&board[y][(x+SIZE-1)%SIZE]; break;
-					}
-					*ptr=board[y][x];
-					board[y][x]=nullptr;
-					break;
+			if(board[y][x]&&board[y][x]->active){
+				candidates.emplace_back(x,y);
+			}
+		}
+	}
+
+	for(const pair<int,int> &p : candidates){
+		int x=p.first,y=p.second;
+		if(board[y][x]->active==0)continue;
+		switch(board[y][x]->tick(*this)){
+			case WorldAction::none: break;
+
+			case WorldAction::die:
+				delete board[y][x];
+				board[y][x]=nullptr;
+				break;
+
+			case WorldAction::move:{
+				Robot** ptr=nullptr;
+				switch(board[y][x]->heading%4){
+					case 0: ptr=&board[(y+SIZE-1)%SIZE][x]; break;
+					case 1: ptr=&board[y][(x+1)%SIZE]; break;
+					case 2: ptr=&board[(y+1)%SIZE][x]; break;
+					case 3: ptr=&board[y][(x+SIZE-1)%SIZE]; break;
 				}
+				*ptr=board[y][x];
+				board[y][x]=nullptr;
+				break;
 			}
 		}
 	}
-- 
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