Create 1970-last-day-where-you-can-still-cross.js

Author: everthis

1970-last-day-where-you-can-still-cross.js

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+/**
+ * @param {number} row
+ * @param {number} col
+ * @param {number[][]} cells
+ * @return {number}
+ */
+const latestDayToCross = function (row, col, cells) {
+  let l = 0,
+    n = cells.length,
+    r = n - 1,
+    res = 0
+  while (l < r) {
+    const mid = ~~((l + r) / 2)
+    if (canWalk(mid)) {
+      l = mid + 1
+      res = mid
+    } else {
+      r = mid
+    }
+  }
+
+  return res + 1
+
+  function canWalk(mid) {
+    const grid = Array.from({ length: row }, () => Array(col).fill(0))
+    const dirs = [
+      [1, 0],
+      [-1, 0],
+      [0, 1],
+      [0, -1],
+    ]
+    for (let i = 0; i <= mid; i++) {
+      const [r, c] = cells[i]
+      grid[r - 1][c - 1] = 1
+    }
+
+    let q = []
+
+    for (let i = 0; i < col; i++) {
+      if (grid[0][i] === 0) {
+        q.push([0, i])
+        grid[0][i] = 1
+      }
+    }
+
+    while (q.length) {
+      const size = q.length,
+        tmp = []
+      for (let i = 0; i < size; i++) {
+        const [r, c] = q[i]
+        if (r === row - 1) return true
+        for (let [dr, dc] of dirs) {
+          const nr = r + dr,
+            nc = c + dc
+          if (nr < 0 || nr >= row || nc < 0 || nc >= col || grid[nr][nc] === 1)
+            continue
+          tmp.push([nr, nc])
+          grid[nr][nc] = 1
+        }
+      }
+      q = tmp
+    }
+
+    return false
+  }
+}