[LeetCode] 061: N-Queens II

[Problem]

Follow up for N-Queens problem.

Now, instead outputting board configurations, return the total number of distinct solutions.

[Solution]

class Solution {
public:
/**
 * if the current position is valid
 */
bool check(int pos[], int level){
for(int i = 0; i < level; ++i){
if(i + pos[i] == level + pos[level] || pos[i] - i == pos[level] - level){
return false;
}
}
return true;
}
/**
 * get total number method to put N Queens
 */
int totalNQueens(int n, bool used[], int pos[], int level){
int res = 0;
// the last level
if(level == n-1){
// set the Queen in n positions
for(int i = 0; i < n; ++i){
pos[level] = i;
if(!used[i] && check(pos, level)){
res++;
}
}
}
// recursion
else{
for(int i = 0; i < n; ++i){
pos[level] = i;
if(!used[i] && check(pos, level)){
used[i] = true;
int nextRes = totalNQueens(n, used, pos, level+1);
res += nextRes;
used[i] = false;
}
}
}
return res;
}
/**
 * total number of methods to put N queens
 */
int totalNQueens(int n) {
// Note: The Solution object is instantiated only once and is reused by each test case.
if(n <= 0)return 0;

// initial
bool used[n];
int pos[n];
memset(used, false, sizeof(used));
return totalNQueens(n, used, pos, 0);
}
};

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