Add lazy versions of pset1

semester3/pset1/7-2-Infix-to-Postfix-Conversion.c

@@ -1,26 +1,122 @@
+// 20:05 - 20:50
 #include <stdio.h>
-#define SIZE 100
+#include <stdlib.h>
+#define MAX 256
+
+int getPriority(char ch) {
+  if (ch == '+' || ch == '-') {
+    return 0;
+  } else if (ch == '*' || ch == '/') {
+    return 1;
+  } else {
+    return -1;
+  }
+}
 
 typedef struct stack {
+  double *arr;
   int top;
-  int capacity;
-  int* array;
 } stack;
 
-void push(stack* st, int val) {
-  st->array[++st->top] = val;
+stack *newStack() {
+  stack *st = malloc(sizeof(stack));
+  st->top = 0;
+  st->arr = malloc(sizeof(double) * MAX);
+
+  return st;
 }
 
-void pop(stack* st) {
-  st->top--;
+void push(stack *st, double val) {
+  // printf("Pushing: %.2lf\n", val);
+  st->arr[st->top++] = val;
 }
 
-int peek(stack* st) {
-  return st->array[st->top];
+double top(stack *st) { return st->arr[st->top - 1]; }
+
+void pop(stack *st) { st->top--; }
+
+int isEmpty(stack *st) { return (st->top == 0); }
+
+void toPostfix(char *buf, char *out) {
+  int count = 0;
+  stack *st = newStack();
+  for (int i = 0; buf[i] != '\0'; i++) {
+    if (buf[i] >= '0' && buf[i] <= '9') {
+      // is digit, push to out array
+      out[count++] = buf[i];
+    } else {
+      if (buf[i] == '(') {
+        // left paren, don't pop elements in stack.
+        push(st, buf[i]);
+      } else if (buf[i] == ')') {
+        // push everything after the (
+        while (top(st) != '(') {
+          out[count++] = top(st);
+          pop(st);
+        }
+        pop(st);
+      } else {
+        // the equal sign is important
+        while (!isEmpty(st) && getPriority(top(st)) >= getPriority(buf[i])) {
+          out[count++] = top(st);
+          pop(st);
+        }
+        push(st, buf[i]);
+      }
+    }
+  }
+
+  while (!isEmpty(st)) {
+    out[count++] = top(st);
+    pop(st);
+  }
+
+  out[count] = '\0';
+}
+
+void calculate(char *postfix) {
+  double l, r;
+  stack *st = newStack();
+  for (int i = 0; postfix[i] != '\0'; i++) {
+    if (postfix[i] >= '0' && postfix[i] <= '9') {
+      // remember convert from char to int
+      push(st, postfix[i] - '0');
+    } else {
+      r = top(st);
+      pop(st);
+      l = top(st);
+      pop(st);
+      if (postfix[i] == '+') {
+        push(st, l + r);
+      } else if (postfix[i] == '-') {
+        push(st, l - r);
+      } else if (postfix[i] == '*') {
+        push(st, l * r);
+      } else if (postfix[i] == '/') {
+        push(st, l / r);
+      } else {
+        printf("ERROR: %c is not recognized\n", postfix[i]);
+      }
+    }
+  }
+
+  printf("%.2lf\n", top(st));
+}
+
+void printPostfix(char *postfix) {
+  for (int i = 0; postfix[i] != '\0'; i++) {
+    printf("%c ", postfix[i]);
+  }
 }
 
 int main(void) {
-  char input[SIZE];
-  
-  fscanf(input, SIZE, stdin);
+  char buf[MAX];
+  char out[MAX];
+
+  scanf("%s", buf);
+
+  toPostfix(buf, out);
+  calculate(out);
+  printPostfix(out);
+  return 0;
 }

semester3/pset1/7-3-central-list-ARRAY.c

@@ -0,0 +1,22 @@
+// 20:50 - 21:00
+#include <stdio.h>
+#define MAX 100
+
+int main(void) {
+  int arr[MAX];
+  int counter = 0;
+  while (scanf("%d,", &arr[counter]) != EOF) {
+    counter++;
+  }
+
+  for (int i = 0, end = counter / 2; i < end; i++) {
+    if (arr[i] != arr[counter - i - 1]) {
+      printf("No");
+      return 0;
+    }
+  }
+
+  printf("Yes");
+
+  return 0;
+}

semester3/pset1/7-4-who-is-the-last-ARRAY.c

@@ -0,0 +1,42 @@
+// 21:01 - 21:21
+#include <stdio.h>
+
+int step(int cur, int *dead, int N, int M) {
+  for (int i = 0; i < M; i++) {
+    cur = (cur + 1) % N;
+    while (dead[cur] == 1) {
+      cur = (cur + 1) % N;
+    }
+  }
+  return cur;
+}
+
+int main(void) {
+  int N, M;
+  scanf("%d,%d", &N, &M);
+
+  int deadCount = 0;
+  int dead[N];
+  for (int i = 0; i < N; i++) {
+    dead[i] = 0;
+  }
+
+  int cur = 0;
+
+  while (1) {
+    cur = step(cur, dead, N, M);
+
+    dead[cur] = 1;
+    deadCount++;
+    if (deadCount == N) {
+      printf("%d", cur + 1);
+      break;
+    } else {
+      printf("%d,", cur + 1);
+    }
+
+    cur = step(cur, dead, N, 1);
+  }
+
+  return 0;
+}