advent2025

commit 6a2844416f21d4c56259a9a6550d05bd883bc4b8
parent 6394f767b86d0a0b421e639f88544d672da5614e
Author: bsandro <email@bsandro.tech>
Date:   Sat, 13 Dec 2025 23:14:18 +0200

day10 p1 basic optimization (using xor)

Diffstat:
M
day10.c
 | 
87
++++++++++++++++++++++++++++++++++---------------------------------------------

1 file changed, 37 insertions(+), 50 deletions(-)
diff --git a/day10.c b/day10.c
@@ -8,7 +8,7 @@
 
 #define BUF_SIZE 256
 
-int btoi(int bufl, char buf[bufl]) {
+static int btoi(int bufl, char buf[bufl]) {
     int num = 0;
     for (int i=0;i<bufl;++i) num = num*10+(buf[i]-'0');
     return num;
@@ -21,32 +21,48 @@ typedef struct {
 
 typedef struct {
     int lights_l;
-    bool lights[16]; //@todo bit field? desired value
-    bool lights1[16];//overall value that we can change
+    bool lights[16];
+    uint16_t indicators;
     int buttons_l;
     Button buttons[16];
+    int buttons1_l;
+    uint16_t buttons1[16];
     int joltages_l;
     int joltages[16]; // same number as lights
 } Machine;
 
-void m_lights_add(Machine *m, int bufl, char buf[bufl]) {
+static void m_lights_add(Machine *m, int bufl, char buf[bufl]) {
     for (int i=0;i<bufl;++i) {
         m->lights[m->lights_l++] = buf[i]=='#';
     }
 }
 
-void m_button_add(Machine *m, int bufl, char buf[bufl]) {
+static void m_indicators_add(Machine *m, int bufl, char buf[bufl]) {
+    for (int i=0;i<bufl;++i) {
+        if (buf[i]=='#') m->indicators |= 1<<i;
+    }
+}
+
+static void m_button_add(Machine *m, int bufl, char buf[bufl]) {
     Button *btn = &m->buttons[m->buttons_l++];
     for (int i=0;i<bufl;++i) {
         btn->toggles[btn->toggles_l++] = buf[i]-'0';
     }
 }
 
-void m_joltage_add(Machine *m, int jolt) {
+static void m_button1_add(Machine *m, int bufl, char buf[bufl]) {
+    int b = m->buttons1_l++;
+    for (int i=0;i<bufl;++i) {
+        m->buttons1[b] |= 1<<(buf[i]-'0');
+    }
+}
+
+static void m_joltage_add(Machine *m, int jolt) {
     m->joltages[m->joltages_l++] = jolt;
 }
 
-bool btn_lights(Button *btn, int light) {
+// used in p2
+static bool btn_lights(Button *btn, int light) {
     for (int i=0;i<btn->toggles_l;++i) {
         if (btn->toggles[i]==light) {
             return true;
@@ -55,54 +71,22 @@ bool btn_lights(Button *btn, int light) {
     return false;
 }
 
-bool m_lights_on(Machine *m) {
-    for (int i=0;i<m->lights_l;++i) {
-        if (m->lights[i]!=m->lights1[i]) return false;
-    }
-    return true;
-}
-
-//@todo use XOR
-void m_light_toggle(Machine *m, int light) {
-    m->lights1[light] = !m->lights1[light];
-}
-
-void m_btn_press(Machine *m, int b) {
-    Button *btn = &m->buttons[b];
-    for (int i=0;i<btn->toggles_l;++i) {
-        m_light_toggle(m, btn->toggles[i]);
-    }
-}
-
-void m_btn_press_many(Machine *m, int comb_l, int comb[comb_l]) {
-    for (int i=0;i<comb_l;++i) {
-        m_btn_press(m, comb[i]);
-    }
-}
-
-bool try_combination(Machine *m, int comb_l, int comb[comb_l], int p) {
+static bool try_combination(Machine *m, int comb_l, uint16_t comb[comb_l], int p) {
     if (p==comb_l) {
-        Machine m1 = *m;
-        m_btn_press_many(&m1, comb_l, comb);
-        if (m_lights_on(&m1)) return true;
-        return false;
+        uint16_t c = 0;
+        for (int i=0;i<comb_l;++i) c ^= comb[i];
+        return m->indicators==c;
     }
-    for (int i=0;i<m->buttons_l;++i) {
-        if (p>0&&comb[p-1]==i) continue; // do not press same button twice in a row
-        comb[p] = i;
-        if (try_combination(m, comb_l, comb, p+1)) {
-            return true;
-        }
+    for (int i=0;i<m->buttons1_l;++i) {
+        uint16_t btn = m->buttons1[i];
+        if (p>0&&comb[p-1]==btn) continue; // do not press same button twice in a row
+        comb[p] = btn;
+        if (try_combination(m, comb_l, comb, p+1)) return true;
     }
     return false;
 }
 
-bool m_try_start(Machine m, int max_presses) {
-    int comb[max_presses];
-    return try_combination(&m, max_presses, comb, 0);
-}
-
-int64_t solve_glpk(Machine *m) {
+static int64_t solve_glpk(Machine *m) {
     int btnl = m->buttons_l;
     int cntl = m->joltages_l;
     // matrix of buttons/counters
@@ -158,10 +142,12 @@ int main(void) {
     for (int c=getchar();c!=EOF;c=getchar()) {
         if (c==']') {
             m_lights_add(&machines[machines_l], bufl, buf);
+            m_indicators_add(&machines[machines_l], bufl, buf);
             bufl = 0;
         }
         else if (c==')') {
             m_button_add(&machines[machines_l], bufl, buf);
+            m_button1_add(&machines[machines_l], bufl, buf);
             bufl = 0;
         }
         else if ((c>='0'&&c<='9')||c=='.'||c=='#') buf[bufl++] = c;
@@ -180,7 +166,8 @@ int main(void) {
     int64_t part2 = 0;
     for (int i=0;i<machines_l;++i) {
         for (int j=1;j<=20;++j) {
-            if (m_try_start(machines[i], j)) {
+            uint16_t comb[j];
+            if (try_combination(&machines[i], j, comb, 0)) {
                 part1 += j;
                 break;
             }