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+---
+title: 第五次作业（答案）
+date: 2020-11-11 22:11:05
+tags:
+---
+
+# P138-17
+
+答案：A对Z，B对X，C对Y
+
+```C
+#include <stdio.h>
+
+int main()
+{
+    int result[3] = { 0, 0, 0 }; // 分别表示ABC三人的对手
+
+    // 分别给ABC指派对手
+    for (int i = 0; i < 3; ++i) { // A
+        result[0] = 'X' + i;
+        for (int j = 0; j < 3; ++j) { // B
+            result[1] = 'X' + j;
+            for (int k = 0; k < 3; ++k) { // C
+                result[2] = 'X' + k;
+                // 检查合法性
+
+                // 两人的对手不能一样
+                if (result[0] == result[1]) {
+                    continue;
+                }
+                if (result[0] == result[2]) {
+                    continue;
+                }
+                if (result[1] == result[2]) {
+                    continue;
+                }
+
+                // A不和X比
+                if (result[0] == 'X') {
+                    continue;
+                }
+
+                // C 不和X，Z比
+                if (result[2] == 'X') {
+                    continue;
+                }
+                if (result[2] == 'Z') {
+                    continue;
+                }
+
+                // 剩下的就是正确答案
+                printf("A的对手是%c\n", result[0]);
+                printf("B的对手是%c\n", result[1]);
+                printf("C的对手是%c\n", result[2]);
+            }
+        }
+    }
+    return 0;
+}
+```
+
+# 二分查找
+
+```C
+#include <stdio.h>
+
+int main()
+{
+    int a[100];
+
+    printf("二分查找");
+    int n;
+    printf("请输入n：\nn = ");
+    scanf("%d", &n);
+    printf("请输入n个有序数（从小到大）：\n");
+    for (int i = 0; i < n; ++i) {
+        scanf("%d", a + i);
+    }
+    printf("请输入你要找的数：");
+    int m;
+    scanf("%d", &m);
+
+    int l = 0;
+    int r = n - 1;
+    while (1) {
+        if (l == r) {
+            if (m == a[l]) {
+                printf("a[%d] = %d\n", l, m);
+            } else if (m < a[l]) {
+                for (int i = n - 1; i >= l; --i) {
+                    a[i + 1] = a[i];
+                }
+                a[l] = m;
+                printf("%d被插入到了a[%d]的位置\n", m, l);
+                for (int i = 0; i < n + 1; ++i) {
+                    printf("a[%d] = %d\n", i, a[i]);
+                }
+            } else {
+                for (int i = n - 1; i >= l + 1; --i) {
+                    a[i + 1] = a[i];
+                }
+                a[l + 1] = m;
+                printf("%d被插入到了a[%d]的位置\n", m, l + 1);
+                for (int i = 0; i < n + 1; ++i) {
+                    printf("a[%d] = %d\n", i, a[i]);
+                }
+            }
+            break;
+        } else if (r == l + 1) {
+            if (m == a[l]) {
+                printf("a[%d] = %d\n", l, m);
+                break;
+            } else if (m < a[l]) {
+                for (int i = n - 1; i >= l; --i) {
+                    a[i + 1] = a[i];
+                }
+                a[l] = m;
+                printf("%d被插入到了a[%d]的位置\n", m, l);
+                for (int i = 0; i < n + 1; ++i) {
+                    printf("a[%d] = %d\n", i, a[i]);
+                }
+                break;
+            } else {
+                l++;
+            }
+        } else {
+            int c = (l + r) / 2;
+            if (m == a[c]) {
+                printf("a[%d] = %d\n", c, m);
+                break;
+            } else if (m < a[c]) {
+                r = c - 1;
+            } else {
+                l = c + 1;
+            }
+        }
+    }
+
+    return 0;
+}
+```
+
+# P165-3
+
+```C
+#include <stdio.h>
+
+int main()
+{
+    int a[3][3];
+    printf("请输入一个3x3的矩阵：\n");
+    for (int i = 0; i < 3; ++i) {
+        for (int j = 0; j < 3; ++j) {
+            scanf("%d", &a[i][j]);
+        }
+    }
+    int sum = a[0][0] + a[0][2] + a[1][1] + a[2][0] + a[2][2];
+
+    printf("对角线元素之和为%d\n", sum);
+
+    return 0;
+}
+```
+
+# P165-6
+
+```C
+#include <stdio.h>
+
+int main()
+{
+    int a[10][10];
+    for (int i = 0; i < 10; ++i) {
+        a[i][0] = 1;
+        a[i][i] = 1;
+    }
+    
+    for (int i = 1; i < 10; ++i) {
+        for (int j = 1; j < i; ++j) {
+            a[i][j] = a[i - 1][j - 1] + a[i - 1][j];
+        }
+    }
+
+    for (int i = 0; i < 10; ++i) {
+        for (int j = 0; j <= i; ++j) {
+            printf("%-5d", a[i][j]);
+        }
+        printf("\n");
+    }
+    
+    return 0;
+}
+```
+
+# P165-10
+
+```C
+#include <stdio.h>
+
+int main()
+{
+    int upper = 0, lower = 0, num = 0, space = 0, others = 0;
+    for (int i = 0; i < 80; ++i) {
+        int c = getchar();
+
+        if (c == ' ') {
+            space++;
+            continue;
+        }
+        if (c >= 'a' && c <= 'z') {
+            lower++;
+            continue;
+        }
+        if (c >= 'A' && c <= 'Z') {
+            upper++;
+            continue;
+        }
+        if (c >= '0' && c <= '9') {
+            num++;
+            continue;
+        }
+        others++;
+    }
+    printf("大写字母有%d\n", upper);
+    printf("小写字母有%d\n", lower);
+    printf("数字有%d\n", num);
+    printf("空格%d\n", space);
+    printf("其它字符有%d\n", others);
+    return 0;
+}
+```