第七课选做题。

07/Optional01.c

@@ -0,0 +1,12 @@
+#include <stdio.h>
+#include <math.h>
+
+int main() {
+    int i = 1;
+    double count = 0;
+    for (; i < 1001; i++) {
+        count += log10(i);
+    }
+    printf("1000! has %d digits.", ((int)count) + 1);
+    return 0;
+}

07/Optional02.c

@@ -0,0 +1,14 @@
+#include <stdio.h>
+
+int main() {
+    int a, b, n, count=0;
+    printf("Please input a, b, n: ");
+    scanf("%d %d %d", &a, &b, &n);
+    for (;n>0;n--) {
+        count += a*b;
+        a--;
+        b--;
+    }
+    printf("The total number is %d", count);
+    return 0;
+}

07/Optional03.c

@@ -0,0 +1,60 @@
+#include <stdio.h>
+#include <stdbool.h>
+
+bool digits[10] = { 0 };
+
+bool checkDigit(int origin, int toBeChecked) {
+    bool originDigit[10] = { 0 }, toBeCheckedDigit[10] = { 0 };
+    int i = 0;
+    while (toBeChecked > 0) {
+        if (toBeCheckedDigit[toBeChecked % 10] == true) {
+            return false;
+        }
+        else {
+            toBeCheckedDigit[toBeChecked % 10] = true;
+        }
+        toBeChecked /= 10;
+    }
+    while (origin > 0) {
+        originDigit[origin % 10] = true;
+        origin /= 10;
+    }
+    while (i < 10) {
+        if (originDigit[i] != toBeCheckedDigit[i]) {
+            return false;
+        }
+        i++;
+    }
+    return true;
+}
+
+void pickDigit(int layer, int picked) {
+    int i = 0;
+    if (layer == 7) {
+        // printf("%d\n", picked);
+        if (checkDigit(picked, 2 * picked) && checkDigit(picked, 3 * picked)) {
+            printf("%d\n", picked);
+        }
+    }
+    else if (layer == 1) {
+        for (i = 1; i <= 3; i++) {
+            digits[i] = true;
+            pickDigit(2, i);
+            digits[i] = false;
+        }
+    }
+    else {
+        for (i = 0; i <= 9; i++) {
+            if (digits[i] == false) {
+                digits[i] = true;
+                pickDigit(layer + 1, picked * 10 + i);
+                digits[i] = false;
+            }
+        }
+    }
+}
+
+int main() {
+    pickDigit(1, 0);
+    return 0;
+}

07/Optional04.c

@@ -0,0 +1,42 @@
+#include <stdio.h>
+#include <stdbool.h>
+
+int pickedColor[6] = { 0 };
+
+bool pickNextColor(int layer, int maxColorCount) {
+	int i = 1;
+	if (layer == 6) {
+		if ((pickedColor[1] != pickedColor[5])
+			&& (pickedColor[1] != pickedColor[4])
+			&& (pickedColor[1] != pickedColor[3])
+			&& (pickedColor[5] != pickedColor[4])
+			&& (pickedColor[3] != pickedColor[4])
+			&& (pickedColor[4] != pickedColor[2])
+			&& (pickedColor[3] != pickedColor[2])) {
+			printf("Min color required: %d\n", maxColorCount);
+			printf("A: %d\nB: %d\nC: %d\nD: %d\nE: %d\n",
+				pickedColor[1], pickedColor[2], pickedColor[3], pickedColor[4], pickedColor[5]);
+			return true;
+		}
+		else {
+			return false;
+		}
+	}
+	else {
+		for (i = 1; i <= maxColorCount; i++) {
+			pickedColor[layer] = i;
+			if (pickNextColor(layer + 1, maxColorCount)) {
+				return true;
+			}
+		}
+		return false;
+	}
+}
+
+int main() {
+	int maxColorCount = 2;
+	while (!pickNextColor(1, maxColorCount)) {
+		maxColorCount++;
+	}
+	return 0;
+}

07/Optional05.c

@@ -0,0 +1,55 @@
+#include <stdio.h>
+#include <stdbool.h>
+
+int numbers[10] = { 0 };
+int cube[3][3] = { 0 };
+
+void output() {
+	int i = 0, j = 0;
+	for (i = 0; i < 3; i++) {
+		for (j = 0; j < 3; j++) {
+			printf("%d", cube[i][j]);
+			printf(" ");
+		}
+		printf("\n");
+	}
+	printf("\n");
+}
+
+void pickNext(int row, int col) {
+	int i = 0;
+	if (row == 2 && col == 2) {
+		for (int i = 1; i <= 9; i++) {
+			if (numbers[i] == false) {
+				cube[2][2] = i;
+				break;
+			}
+		}
+		if ((cube[0][0] + cube[0][1] + cube[0][2] == 15)
+			&& (cube[1][0] + cube[1][1] + cube[1][2] == 15)
+			&& (cube[0][0] + cube[1][0] + cube[2][0] == 15)
+			&& (cube[0][1] + cube[1][1] + cube[2][1] == 15)
+			&& (cube[0][0] + cube[1][1] + cube[2][2] == 15)
+			&& (cube[0][2] + cube[1][1] + cube[2][0] == 15)) {
+			output();
+		}
+	}
+	for (i = 1; i <= 9; i++) {
+		if (numbers[i] == false) {
+			numbers[i] = true;
+			cube[row][col] = i;
+			if (col == 2) {
+				pickNext(row + 1, 0);
+			}
+			else {
+				pickNext(row, col + 1);
+			}
+			numbers[i] = false;
+		}
+	}
+}
+
+int main() {
+	pickNext(0, 0);
+	return 0;
+}