## Thursday, May 24, 2018

### Leetcode 723 Candy Crush

This question is about implementing a basic elimination algorithm for Candy Crush.
Given a 2D integer array `board` representing the grid of candy, different positive integers `board[i][j]`represent different types of candies. A value of `board[i][j] = 0` represents that the cell at position `(i, j)` is empty. The given board represents the state of the game following the player's move. Now, you need to restore the board to a stable state by crushing candies according to the following rules:
1. If three or more candies of the same type are adjacent vertically or horizontally, "crush" them all at the same time - these positions become empty.
2. After crushing all candies simultaneously, if an empty space on the board has candies on top of itself, then these candies will drop until they hit a candy or bottom at the same time. (No new candies will drop outside the top boundary.)
3. After the above steps, there may exist more candies that can be crushed. If so, you need to repeat the above steps.
4. If there does not exist more candies that can be crushed (ie. the board is stable), then return the current board.
You need to perform the above rules until the board becomes stable, then return the current board.
Example 1:
```Input:
board =
[[110,5,112,113,114],[210,211,5,213,214],[310,311,3,313,314],[410,411,412,5,414],[5,1,512,3,3],[610,4,1,613,614],[710,1,2,713,714],[810,1,2,1,1],[1,2,1,2,2],[4,1,4,4,1014]]
Output:
[[0,0,0,0,0],[0,0,0,0,0],[0,0,0,0,0],[110,0,0,0,114],[210,0,0,0,214],[310,0,0,113,314],[410,0,0,213,414],[610,211,112,313,614],[710,311,412,613,714],[810,411,512,713,1014]]
Explanation:

```
Note:
1. The length of `board` will be in the range [3, 50].
2. The length of `board[i]` will be in the range [3, 50].
3. Each `board[i][j]` will initially start as an integer in the range [1, 2000].

https://github.com/joy32812/leetcode/blob/master/src/com/leetcode/P723_CandyCrush.java
int m, n;
int[][] B;

public int[][] candyCrush(int[][] board) {

B = board;
m = B.length;
n = B[0].length;

while (crash()) {
drop();
}

for (int i = 0; i < m; i++) {
for (int j = 0; j < n; j++) {
System.out.print(B[i][j] + " ");
}
System.out.println();
}
return B;
}

private boolean crash() {

boolean[][] c = new boolean[m][n];
for (int i = 0; i < m; i++) {
for (int j = 0; j < n; j++) {
if (B[i][j] == 0)
continue;

int cnt = 1;
// right
for (int k = j + 1; k < n; k++) {
if (B[i][k] == B[i][j])
cnt++;
else
break;
}

if (cnt >= 3) {
for (int k = j; k < n && k < j + cnt; k++) {
c[i][k] = true;
}
}

// down
cnt = 1;
for (int k = i + 1; k < m; k++) {
if (B[i][j] == B[k][j])
cnt++;
else
break;
}

if (cnt >= 3) {
for (int k = i; k < m && k < i + cnt; k++) {
c[k][j] = true;
}
}
}
}

boolean crash = false;
for (int i = 0; i < m; i++) {
for (int j = 0; j < n; j++) {
if (c[i][j]) {
crash = true;
B[i][j] = 0;
}
}
}

return crash;
}

private void drop() {
for (int j = 0; j < n; j++) {

int now = m - 1;
for (int i = m - 1; i >= 0; i--) {
if (B[i][j] == 0)
continue;
int tp = B[i][j];
B[i][j] = B[now][j];
B[now][j] = tp;
now--;
}

}

}
http://www.cnblogs.com/grandyang/p/7858414.html

```    vector<vector<int>> candyCrush(vector<vector<int>>& board) {
int m = board.size(), n = board[0].size();
while (true) {
vector<pair<int, int>> del;
for (int i = 0; i < m; ++i) {
for (int j = 0; j < n; ++j) {
if (board[i][j] == 0) continue;
int x0 = i, x1 = i, y0 = j, y1 = j;
while (x0 >= 0 && x0 > i - 3 && board[x0][j] == board[i][j]) --x0;
while (x1 < m && x1 < i + 3 && board[x1][j] == board[i][j]) ++x1;
while (y0 >= 0 && y0 > j - 3 && board[i][y0] == board[i][j]) --y0;
while (y1 < n && y1 < j + 3 && board[i][y1] == board[i][j]) ++y1;
if (x1 - x0 > 3 || y1 - y0 > 3) del.push_back({i, j});
}
}
if (del.empty()) break;
for (auto a : del) board[a.first][a.second] = 0;
for (int j = 0; j < n; ++j) {
int t = m - 1;
for (int i = m - 1; i >= 0; --i) {
if (board[i][j]) swap(board[t--][j], board[i][j]);
}
}
}
return board;
}```
https://www.codetd.com/article/154114

vector<vector<int>> candyCrush(vector<vector<int>>& board) { int m = board.size(); int n = board[0].size(); while (true) { vector<pair<int, int>> to_crash; for (int i = 0; i < m; i++) { for (int j = 0; j < n; j++) { if (board[i][j]) { //为了减小计算量,元素为0的略过 int i1 = i, i0 = i, j1 = j, j0 = j; // i1,i0,j1,j0分别为向下,向上,向右,向左的检测 //对每个点(i,j),以其为中心,向上下或左右方向扩展,看是否有连续 while (i1 < m && i1 < i+3 && board[i1][j] == board[i][j]) i1++; while (i0 >= 0 && i0 > i-3 && board[i0][j] == board[i][j]) i0--; while (j1 < n && j1 < j+3 && board[i][j1] == board[i][j]) j1++; while (j0 >= 0 && j0 > j-3 && board[i][j0] == board[i][j]) j0--; if (i1-i0 > 3 || j1-j0 > 3) to_crash.push_back({i,j}); //上下或左右连续元素超过3,即符合 } } } if (to_crash.empty()) break; for (auto t : to_crash) board[t.first][t.second] = 0; //重点:将所有标记位置置0 for (int j = 0; j < n; j++) { //由于是自上往下消除,因此外层对j(纵坐标)循环 int t = m-1; //t用于记录新board的横坐标 for (int i = m-1; i >= 0; i--) { //从下往上,非0元素参与交换,每次交换后t上移 if (board[i][j]) swap(board[i][j], board[t--][j]); } } } return board; }
https://www.cnblogs.com/jxr041100/p/8440349.html
```public int[][] candyCrush(int[][] board) {
if (board == null || board.length == 0 || board[0].length == 0) return board;
int cnt = 0;
int m = board.length, n = board[0].length;
for (int i = 0; i < m; i++) {
for (int j = 0; j < n; j++) {
if (board[i][j] == 0) continue;
if (   (i > 0 && Math.abs(board[i-1][j]) == board[i][j] && (i < m - 1 && board[i+1][j] == board[i][j]))
|| (i > 1 && Math.abs(board[i-1][j]) == board[i][j] && Math.abs(board[i-2][j]) == board[i][j])
|| (i < m - 2 && board[i+1][j] == board[i][j] && board[i+2][j] == board[i][j])
|| (j > 0 && Math.abs(board[i][j-1]) == board[i][j] && (j < n - 1 && board[i][j+1] == board[i][j]))
|| (j > 1 && Math.abs(board[i][j-1]) == board[i][j] && Math.abs(board[i][j-2]) == board[i][j])
|| (j < n - 2 && board[i][j+1] == board[i][j] && board[i][j+2] == board[i][j])) {
cnt++;
board[i][j] = -board[i][j];
}
}
}
for (int j = 0; j < n; j++) {
int ptr = m - 1;
for (int i = m - 1; i >= 0; i--) {
if (board[i][j] > 0) {
board[ptr--][j] = board[i][j];
}
}
for (int i = ptr; i >= 0; i--) {
board[i][j] = 0;
}
}
if (cnt == 0) {
return board;
} else {
return candyCrush(board);
}
}```
https://www.cnblogs.com/lightwindy/p/9744174.html
`    ``vector<vector<``int``>> candyCrush(vector<vector<``int``>>& board) {`
`        ``const` `auto` `R = board.size(), C = board[0].size();`
`        ``bool` `changed = ``true``;`
`        `
`        ``while` `(changed) {`
`            ``changed = ``false``;`
`            `
`            ``for` `(``int` `r = 0; r < R; ++r) {`
`                ``for` `(``int` `c = 0; c + 2 < C; ++c) {`
`                    ``auto` `v = ``abs``(board[r][c]);`
`                    ``if` `(v != 0 && v == ``abs``(board[r][c + 1]) && v == ``abs``(board[r][c + 2])) {`
`                        ``board[r][c] = board[r][c + 1] = board[r][c + 2] = -v;`
`                        ``changed = ``true``;`
`                    ``}`
`                ``}`
`            ``}`
`            `
`            ``for` `(``int` `r = 0; r + 2 < R; ++r) {`
`                ``for` `(``int` `c = 0; c < C; ++c) {`
`                    ``auto` `v = ``abs``(board[r][c]);`
`                    ``if` `(v != 0 && v == ``abs``(board[r + 1][c]) && v == ``abs``(board[r + 2][c])) {`
`                        ``board[r][c] = board[r + 1][c] = board[r + 2][c] = -v;`
`                        ``changed = ``true``;`
`                    ``}`
`                ``}`
`            ``}`
`            ``for` `(``int` `c = 0; c < C; ++c) {`
`                ``int` `empty_r = R - 1;`
`                ``for` `(``int` `r = R - 1; r >= 0; --r) {`
`                    ``if` `(board[r][c] > 0) {`
`                        ``board[empty_r--][c] = board[r][c];`
`                    ``}`
`                ``}`
`                ``for` `(``int` `r = empty_r; r >= 0; --r) {`
`                    ``board[r][c] = 0;`
`                ``}`
`            ``}`
`        ``}`
`        `
`        ``return` `board;`
`    ``}`

X. http://storypku.com/2017/11/leetcode-question-723-candy-crush/
vector<vector<int>> candyCrush(vector<vector<int>>& board) {
int m = board.size(), n = board[0].size();
bool toBeContinued = false;

for (int i = 0; i < m; ++i) { // horizontal crushing
for (int j = 0; j + 2 < n; ++j) {
int& v1 = board[i][j];
int& v2 = board[i][j+1];
int& v3 = board[i][j+2];

int v0 = std::abs(v1);

if (v0 && v0 == std::abs(v2) && v0 == std::abs(v3)) {
v1 = v2 = v3 = - v0;
toBeContinued =  true;
}
}
}

for (int i = 0; i + 2 < m; ++i) {  // vertical crushing
for (int j = 0; j < n; ++j) {
int& v1 = board[i][j];
int& v2 = board[i+1][j];
int& v3 = board[i+2][j];
int v0 = std::abs(v1);
if (v0 && v0 == std::abs(v2) && v0 == std::abs(v3)) {
v1 = v2 = v3 = -v0;
toBeContinued = true;
}
}
}

for (int j = 0; j < n; ++j) { // gravity step
int dropTo = m - 1;
for (int i = m - 1; i >= 0; --i) {
if (board[i][j] >= 0) {
board[dropTo--][j] = board[i][j];
}
}

for (int i = dropTo; i >= 0; i--) {
board[i][j] = 0;
}
}

}