添加 0051.N皇后.md C语言版本

problems/0051.N皇后.md

@@ -521,5 +521,130 @@ func solveNQueens(_ n: Int) -> [[String]] {
 }
 ```
 
+### C
+```c
+char ***ans;
+char **path;
+int ansTop, pathTop;
+//将path中元素复制到ans中
+void copyPath(int n) {
+    char **tempPath = (char**)malloc(sizeof(char*) * pathTop);
+    int i;
+    for(i = 0; i < pathTop; ++i) {
+        tempPath[i] = (char*)malloc(sizeof(char) * n + 1);
+        int j;
+        for(j = 0; j < n; ++j)
+            tempPath[i][j] = path[i][j];
+        tempPath[i][j] = '\0';
+
+    }
+    ans[ansTop++] = tempPath;
+}
+
+//判断当前位置是否有效（是否不被其它皇后影响）
+int isValid(int x, int y, int n) {
+    int i, j;
+    //检查同一行以及同一列是否有效
+    for(i = 0; i < n; ++i) {
+        if(path[y][i] == 'Q' || path[i][x] == 'Q')
+            return 0;
+    }
+    //下面两个for循环检查斜角45度是否有效
+    i = y - 1;
+    j = x - 1;
+    while(i >= 0 && j >= 0) {
+        if(path[i][j] == 'Q')
+            return 0;
+        --i, --j;
+    }
+
+    i = y + 1;
+    j = x + 1;
+    while(i < n && j < n) {
+        if(path[i][j] == 'Q')
+            return 0;
+        ++i, ++j;
+    }
+
+    //下面两个for循环检查135度是否有效
+    i = y - 1;
+    j = x + 1;
+    while(i >= 0 && j < n) {
+        if(path[i][j] == 'Q')
+            return 0;
+        --i, ++j;
+    }
+
+    i = y + 1;
+    j = x -1;
+    while(j >= 0 && i < n) {
+        if(path[i][j] == 'Q')
+            return 0;
+        ++i, --j;
+    }
+    return 1;
+}
+
+void backTracking(int n, int depth) {
+    //若path中有四个元素，将其拷贝到ans中。从当前层返回
+    if(pathTop == n) {
+        copyPath(n);
+        return;
+    }
+
+    //遍历横向棋盘
+    int i;
+    for(i = 0; i < n; ++i) {
+        //若当前位置有效
+        if(isValid(i, depth, n)) {
+            //在当前位置放置皇后
+            path[depth][i] = 'Q';
+            //path中元素数量+1
+            ++pathTop;
+
+            backTracking(n, depth + 1);
+            //进行回溯
+            path[depth][i] = '.';
+            //path中元素数量-1
+            --pathTop;
+        }
+    }
+}
+
+//初始化存储char*数组path，将path中所有元素设为'.'
+void initPath(int n) {
+    int i, j;
+    for(i = 0; i < n; i++) {
+        //为path中每个char*开辟空间
+        path[i] = (char*)malloc(sizeof(char) * n + 1);
+        //将path中所有字符设为'.'
+        for(j = 0; j < n; j++)
+            path[i][j] = '.';
+        //在每个字符串结尾加入'\0'
+        path[i][j] = '\0';
+    }
+}
+
+char *** solveNQueens(int n, int* returnSize, int** returnColumnSizes){
+    //初始化辅助变量
+    ans = (char***)malloc(sizeof(char**) * 400);
+    path = (char**)malloc(sizeof(char*) * n);
+    ansTop = pathTop = 0;
+
+    //初始化path数组
+    initPath(n);
+    backTracking(n, 0);
+
+    //设置返回数组大小
+    *returnSize = ansTop;
+    int i; 
+    *returnColumnSizes = (int*)malloc(sizeof(int) * ansTop);
+    for(i = 0; i < ansTop; ++i) {
+        (*returnColumnSizes)[i] = n;
+    }
+    return ans;
+}
+```
+
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